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16.1 Introduction to Spring Web MVC framework
The Spring Web model-view-controller (MVC) framework is designed around a
DispatcherServlet that dispatches requests to handlers, with configurable handler
mappings, view resolution, locale, time zone and theme resolution as well as support for
uploading files. The default handler is based on the @Controller and @RequestMapping
annotations, offering a wide range of flexible handling methods. With the introduction
of Spring 3.0, the @Controller mechanism also allows you to create RESTful Web sites
and applications, through the @PathVariable annotation and other features.
In Spring Web MVC you can use any object as a command or form-backing object; you do not
need to implement a framework-specific interface or base class. Spring’s data binding is
highly flexible: for example, it treats type mismatches as validation errors that can be
evaluated by the application, not as system errors. Thus you need not duplicate your
business objects' properties as simple, untyped strings in your form objects simply to
handle invalid submissions, or to convert the Strings properly. Instead, it is often
preferable to bind directly to your business objects.
Spring’s view resolution is extremely flexible. A Controller is typically responsible
for preparing a model Map with data and selecting a view name but it can also write
directly to the response stream and complete the request. View name resolution is highly
configurable through file extension or Accept header content type negotiation, through
bean names, a properties file, or even a custom ViewResolver implementation. The model
(the M in MVC) is a Map interface, which allows for the complete abstraction of the
view technology. You can integrate directly with template based rendering technologies
such as JSP, Velocity and Freemarker, or directly generate XML, JSON, Atom, and many
other types of content. The model Map is simply transformed into an appropriate
format, such as JSP request attributes, a Velocity template model.
16.1.1 Features of Spring Web MVC
Spring’s web module includes many unique web support features:
-
Clear separation of roles. Each role — controller, validator, command object,
form object, model object,
DispatcherServlet , handler mapping, view resolver, and so
on — can be fulfilled by a specialized object.
-
Powerful and straightforward configuration of both framework and application classes
as JavaBeans. This configuration capability includes easy referencing across
contexts, such as from web controllers to business objects and validators.
-
Adaptability, non-intrusiveness, and flexibility. Define any controller method
signature you need, possibly using one of the parameter annotations (such as
@RequestParam, @RequestHeader, @PathVariable, and more) for a given scenario.
-
Reusable business code, no need for duplication. Use existing business objects
as command or form objects instead of mirroring them to extend a particular framework
base class.
-
Customizable binding and validation. Type mismatches as application-level
validation errors that keep the offending value, localized date and number binding,
and so on instead of String-only form objects with manual parsing and conversion to
business objects.
-
Customizable handler mapping and view resolution. Handler mapping and view
resolution strategies range from simple URL-based configuration, to sophisticated,
purpose-built resolution strategies. Spring is more flexible than web MVC frameworks
that mandate a particular technique.
-
Flexible model transfer. Model transfer with a name/value
Map supports easy
integration with any view technology.
-
Customizable locale, time zone and theme resolution, support for JSPs with or without
Spring tag library, support for JSTL, support for Velocity without the need for extra
bridges, and so on.
-
A simple yet powerful JSP tag library known as the Spring tag library that provides
support for features such as data binding and themes. The custom tags allow for
maximum flexibility in terms of markup code. For information on the tag library
descriptor, see the appendix entitled Chapter 35, spring.tld
-
A JSP form tag library, introduced in Spring 2.0, that makes writing forms in JSP
pages much easier. For information on the tag library descriptor, see the appendix
entitled Chapter 36, spring-form.tld
-
Beans whose lifecycle is scoped to the current HTTP request or HTTP
Session .
This is not a specific feature of Spring MVC itself, but rather of the
WebApplicationContext container(s) that Spring MVC uses. These bean scopes are
described in Section 4.5.4, “Request, session, and global session scopes”
16.1.2 Pluggability of other MVC implementations
Non-Spring MVC implementations are preferable for some projects. Many teams expect to
leverage their existing investment in skills and tools, for example with JSF.
If you do not want to use Spring’s Web MVC, but intend to leverage other solutions that
Spring offers, you can integrate the web MVC framework of your choice with Spring
easily. Simply start up a Spring root application context through its
ContextLoaderListener , and access it through its ServletContext attribute (or
Spring’s respective helper method) from within any action object. No "plug-ins"
are involved, so no dedicated integration is necessary. From the web layer’s point of
view, you simply use Spring as a library, with the root application context instance as
the entry point.
Your registered beans and Spring’s services can be at your fingertips even without
Spring’s Web MVC. Spring does not compete with other web frameworks in this scenario.
It simply addresses the many areas that the pure web MVC frameworks do not, from bean
configuration to data access and transaction handling. So you can enrich your
application with a Spring middle tier and/or data access tier, even if you just want
to use, for example, the transaction abstraction with JDBC or Hibernate.
16.2 The DispatcherServlet
Spring’s web MVC framework is, like many other web MVC frameworks, request-driven,
designed around a central Servlet that dispatches requests to controllers and offers
other functionality that facilitates the development of web applications. Spring’s
DispatcherServlet however, does more than just that. It is completely integrated with
the Spring IoC container and as such allows you to use every other feature that Spring
has.
The request processing workflow of the Spring Web MVC DispatcherServlet is illustrated
in the following diagram. The pattern-savvy reader will recognize that the
DispatcherServlet is an expression of the "Front Controller" design pattern (this is a
pattern that Spring Web MVC shares with many other leading web frameworks).
The request processing workflow in Spring Web MVC (high level)
The DispatcherServlet is an actual Servlet (it inherits from the HttpServlet base
class), and as such is declared in the web.xml of your web application. You need to
map requests that you want the DispatcherServlet to handle, by using a URL mapping in
the same web.xml file. This is standard Java EE Servlet configuration; the following
example shows such a DispatcherServlet declaration and mapping:
<web-app>
<servlet>
<servlet-name>example</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>example</servlet-name>
<url-pattern>/example/*</url-pattern>
</servlet-mapping>
</web-app>
In the preceding example, all requests starting with /example will be handled by the
DispatcherServlet instance named example . In a Servlet 3.0+ environment, you also
have the option of configuring the Servlet container programmatically. Below is the code
based equivalent of the above web.xml example:
public class MyWebApplicationInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext container) {
ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet());
registration.setLoadOnStartup(1);
registration.addMapping("/example/*");
}
}
WebApplicationInitializer is an interface provided by Spring MVC that ensures your
code-based configuration is detected and automatically used to initialize any Servlet 3
container. An abstract base class implementation of this interace named
AbstractDispatcherServletInitializer makes it even easier to register the
DispatcherServlet by simply specifying its servlet mapping.
See Code-based Servlet container initialization for more details.
The above is only the first step in setting up Spring Web MVC. You now need to configure
the various beans used by the Spring Web MVC framework (over and above the
DispatcherServlet itself).
As detailed in Section 4.16, “Additional Capabilities of the ApplicationContext”, ApplicationContext instances in Spring can be
scoped. In the Web MVC framework, each DispatcherServlet has its own
WebApplicationContext , which inherits all the beans already defined in the root
WebApplicationContext . These inherited beans can be overridden in the servlet-specific
scope, and you can define new scope-specific beans local to a given Servlet instance.
Upon initialization of a DispatcherServlet , Spring MVC looks for a file named
[servlet-name]-servlet.xml in the WEB-INF directory of your web application and
creates the beans defined there, overriding the definitions of any beans defined with
the same name in the global scope.
Consider the following DispatcherServlet Servlet configuration (in the web.xml file):
<web-app>
<servlet>
<servlet-name>golfing</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>golfing</servlet-name>
<url-pattern>/golfing/*</url-pattern>
</servlet-mapping>
</web-app>
With the above Servlet configuration in place, you will need to have a file called
/WEB-INF/golfing-servlet.xml in your application; this file will contain all of your
Spring Web MVC-specific components (beans). You can change the exact location of this
configuration file through a Servlet initialization parameter (see below for details).
It is also possible to have just one root context for single DispatcherServlet scenarios
by setting an empty contextConfigLocation servlet init parameter, as shown below:
<web-app>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/root-context.xml</param-value>
</context-param>
<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value></param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
</web-app>
The WebApplicationContext is an extension of the plain ApplicationContext that has
some extra features necessary for web applications. It differs from a normal
ApplicationContext in that it is capable of resolving themes (see
Section 16.10, “Using themes”), and that it knows which Servlet it is associated with (by having
a link to the ServletContext ). The WebApplicationContext is bound in the
ServletContext , and by using static methods on the RequestContextUtils class you can
always look up the WebApplicationContext if you need access to it.
16.2.1 Special Bean Types In the WebApplicationContext
The Spring DispatcherServlet uses special beans to process requests and render the
appropriate views. These beans are part of Spring MVC. You can choose which special
beans to use by simply configuring one or more of them in the WebApplicationContext .
However, you don’t need to do that initially since Spring MVC maintains a list of
default beans to use if you don’t configure any. More on that in the next section. First
see the table below listing the special bean types the DispatcherServlet relies on.
Table 16.1. Special bean types in the WebApplicationContext
Bean type | Explanation |
---|
HandlerMapping | Maps incoming requests to handlers and a list of pre- and post-processors (handler
interceptors) based on some criteria the details of which vary by HandlerMapping
implementation. The most popular implementation supports annotated controllers but
other implementations exists as well. | HandlerAdapter | Helps the DispatcherServlet to invoke a handler mapped to a request regardless of
the handler is actually invoked. For example, invoking an annotated controller
requires resolving various annotations. Thus the main purpose of a HandlerAdapter is
to shield the DispatcherServlet from such details. | HandlerExceptionResolver | Maps exceptions to views also allowing for more complex exception handling code. | ViewResolver | Resolves logical String-based view names to actual View types. | LocaleResolver & LocaleContextResolver | Resolves the locale a client is using and possibly their time zone, in order to be able
to offer internationalized views | ThemeResolver | Resolves themes your web application can use, for example, to offer personalized layouts | MultipartResolver | Parses multi-part requests for example to support processing file uploads from HTML
forms. | FlashMapManager | Stores and retrieves the "input" and the "output" FlashMap that can be used to pass
attributes from one request to another, usually across a redirect. |
16.2.2 Default DispatcherServlet Configuration
As mentioned in the previous section for each special bean the DispatcherServlet
maintains a list of implementations to use by default. This information is kept in the
file DispatcherServlet.properties in the package org.springframework.web.servlet .
All special beans have some reasonable defaults of their own. Sooner or later though
you’ll need to customize one or more of the properties these beans provide. For example
it’s quite common to configure an InternalResourceViewResolver settings its prefix
property to the parent location of view files.
Regardless of the details, the important concept to understand here is that once
you configure a special bean such as an InternalResourceViewResolver in your
WebApplicationContext , you effectively override the list of default implementations
that would have been used otherwise for that special bean type. For example if you
configure an InternalResourceViewResolver , the default list of ViewResolver
implementations is ignored.
In Section 16.16, “Configuring Spring MVC” you’ll learn about other options for configuring Spring MVC including
MVC Java config and the MVC XML namespace both of which provide a simple starting point
and assume little knowledge of how Spring MVC works. Regardless of how you choose to
configure your application, the concepts explained in this section are fundamental
should be of help to you.
16.2.3 DispatcherServlet Processing Sequence
After you set up a DispatcherServlet , and a request comes in for that specific
DispatcherServlet , the DispatcherServlet starts processing the request as follows:
-
The
WebApplicationContext is searched for and bound in the request as an attribute
that the controller and other elements in the process can use. It is bound by default
under the key DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE .
-
The locale resolver is bound to the request to enable elements in the process to
resolve the locale to use when processing the request (rendering the view, preparing
data, and so on). If you do not need locale resolving, you do not need it.
-
The theme resolver is bound to the request to let elements such as views determine
which theme to use. If you do not use themes, you can ignore it.
-
If you specify a multipart file resolver, the request is inspected for multiparts; if
multiparts are found, the request is wrapped in a
MultipartHttpServletRequest for
further processing by other elements in the process. See Section 16.11, “Spring’s multipart (file upload) support” for further
information about multipart handling.
-
An appropriate handler is searched for. If a handler is found, the execution chain
associated with the handler (preprocessors, postprocessors, and controllers) is
executed in order to prepare a model or rendering.
-
If a model is returned, the view is rendered. If no model is returned, (may be due to
a preprocessor or postprocessor intercepting the request, perhaps for security
reasons), no view is rendered, because the request could already have been fulfilled.
Handler exception resolvers that are declared in the WebApplicationContext pick up
exceptions that are thrown during processing of the request. Using these exception
resolvers allows you to define custom behaviors to address exceptions.
The Spring DispatcherServlet also supports the return of the
last-modification-date, as specified by the Servlet API. The process of determining
the last modification date for a specific request is straightforward: the
DispatcherServlet looks up an appropriate handler mapping and tests whether the
handler that is found implements the LastModified interface. If so, the value of the
long getLastModified(request) method of the LastModified interface is returned to
the client.
You can customize individual DispatcherServlet instances by adding Servlet
initialization parameters ( init-param elements) to the Servlet declaration in the
web.xml file. See the following table for the list of supported parameters.
Table 16.2. DispatcherServlet initialization parameters
Parameter | Explanation |
---|
contextClass
| Class that implements WebApplicationContext , which instantiates the context used by
this Servlet. By default, the XmlWebApplicationContext is used. | contextConfigLocation
| String that is passed to the context instance (specified by contextClass ) to
indicate where context(s) can be found. The string consists potentially of multiple
strings (using a comma as a delimiter) to support multiple contexts. In case of
multiple context locations with beans that are defined twice, the latest location
takes precedence. | namespace
| Namespace of the WebApplicationContext . Defaults to [servlet-name]-servlet . |
16.3 Implementing Controllers
Controllers provide access to the application behavior that you typically define through
a service interface. Controllers interpret user input and transform it into a model that
is represented to the user by the view. Spring implements a controller in a very
abstract way, which enables you to create a wide variety of controllers.
Spring 2.5 introduced an annotation-based programming model for MVC controllers that
uses annotations such as @RequestMapping , @RequestParam , @ModelAttribute , and so
on. This annotation support is available for both Servlet MVC and Portlet MVC.
Controllers implemented in this style do not have to extend specific base classes or
implement specific interfaces. Furthermore, they do not usually have direct dependencies
on Servlet or Portlet APIs, although you can easily configure access to Servlet or
Portlet facilities.
![[Tip]](images/tip.png) | Tip |
---|
Available in the spring-projects Org on Github,
a number of web applications leverage the annotation support described in this section
including MvcShowcase, MvcAjax, MvcBasic, PetClinic, PetCare,
and others.
|
@Controller
public class HelloWorldController {
@RequestMapping("/helloWorld")
public String helloWorld(Model model) {
model.addAttribute("message", "Hello World!");
return "helloWorld";
}
}
As you can see, the @Controller and @RequestMapping annotations allow flexible
method names and signatures. In this particular example the method accepts a Model and
returns a view name as a String , but various other method parameters and return values
can be used as explained later in this section. @Controller and @RequestMapping and
a number of other annotations form the basis for the Spring MVC implementation. This
section documents these annotations and how they are most commonly used in a Servlet
environment.
16.3.1 Defining a controller with @Controller
The @Controller annotation indicates that a particular class serves the role of
a controller. Spring does not require you to extend any controller base class or
reference the Servlet API. However, you can still reference Servlet-specific features if
you need to.
The @Controller annotation acts as a stereotype for the annotated class, indicating
its role. The dispatcher scans such annotated classes for mapped methods and detects
@RequestMapping annotations (see the next section).
You can define annotated controller beans explicitly, using a standard Spring bean
definition in the dispatcher’s context. However, the @Controller stereotype also
allows for autodetection, aligned with Spring general support for detecting component
classes in the classpath and auto-registering bean definitions for them.
To enable autodetection of such annotated controllers, you add component scanning to
your configuration. Use the spring-context schema as shown in the following XML
snippet:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="org.springframework.samples.petclinic.web"/>
</beans>
16.3.2 Mapping Requests With @RequestMapping
You use the @RequestMapping annotation to map URLs such as /appointments onto an
entire class or a particular handler method. Typically the class-level annotation maps a
specific request path (or path pattern) onto a form controller, with additional
method-level annotations narrowing the primary mapping for a specific HTTP method
request method ("GET", "POST", etc.) or an HTTP request parameter condition.
The following example from the Petcare sample shows a controller in a Spring MVC
application that uses this annotation:
@Controller
@RequestMapping("/appointments")
public class AppointmentsController {
private final AppointmentBook appointmentBook;
@Autowired
public AppointmentsController(AppointmentBook appointmentBook) {
this.appointmentBook = appointmentBook;
}
@RequestMapping(method = RequestMethod.GET)
public Map<String, Appointment> get() {
return appointmentBook.getAppointmentsForToday();
}
@RequestMapping(value="/{day}", method = RequestMethod.GET)
public Map<String, Appointment> getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) {
return appointmentBook.getAppointmentsForDay(day);
}
@RequestMapping(value="/new", method = RequestMethod.GET)
public AppointmentForm getNewForm() {
return new AppointmentForm();
}
@RequestMapping(method = RequestMethod.POST)
public String add(@Valid AppointmentForm appointment, BindingResult result) {
if (result.hasErrors()) {
return "appointments/new";
}
appointmentBook.addAppointment(appointment);
return "redirect:/appointments";
}
}
In the example, the @RequestMapping is used in a number of places. The first usage is
on the type (class) level, which indicates that all handling methods on this controller
are relative to the /appointments path. The get() method has a further
@RequestMapping refinement: it only accepts GET requests, meaning that an HTTP GET for
/appointments invokes this method. The add() has a similar refinement, and the
getNewForm() combines the definition of HTTP method and path into one, so that GET
requests for appointments/new are handled by that method.
The getForDay() method shows another usage of @RequestMapping : URI templates. (See
the next section).
A @RequestMapping on the class level is not required. Without it, all paths are simply
absolute, and not relative. The following example from the PetClinic sample
application shows a multi-action controller using @RequestMapping :
@Controller
public class ClinicController {
private final Clinic clinic;
@Autowired
public ClinicController(Clinic clinic) {
this.clinic = clinic;
}
@RequestMapping("/")
public void welcomeHandler() {
}
@RequestMapping("/vets")
public ModelMap vetsHandler() {
return new ModelMap(this.clinic.getVets());
}
}
@Controller 's and AOP Proxying
In some cases a controller may need to be decorated with an AOP proxy at runtime.
One example is if you choose to have @Transactional annotations directly on the
controller. When this is the case, for controllers specifically, we recommend
using class-based proxying. This is typically the default choice with controllers.
However if a controller must implement an interface that is not a Spring Context
callback (e.g. InitializingBean , *Aware , etc), you may need to explicitly
configure class-based proxying. For example with <tx:annotation-driven /> ,
change to <tx:annotation-driven proxy-target-class="true" /> .
New Support Classes for @RequestMapping methods in Spring MVC 3.1
Spring 3.1 introduced a new set of support classes for @RequestMapping methods called
RequestMappingHandlerMapping and RequestMappingHandlerAdapter respectively. They are
recommended for use and even required to take advantage of new features in Spring MVC
3.1 and going forward. The new support classes are enabled by default by the MVC
namespace and the MVC Java config but must be configured explicitly if using neither.
This section describes a few important differences between the old and the new support
classes.
Prior to Spring 3.1, type and method-level request mappings were examined in two
separate stages — a controller was selected first by the
DefaultAnnotationHandlerMapping and the actual method to invoke was narrowed down
second by the AnnotationMethodHandlerAdapter .
With the new support classes in Spring 3.1, the RequestMappingHandlerMapping is the
only place where a decision is made about which method should process the request. Think
of controller methods as a collection of unique endpoints with mappings for each method
derived from type and method-level @RequestMapping information.
This enables some new possibilities. For once a HandlerInterceptor or a
HandlerExceptionResolver can now expect the Object-based handler to be a
HandlerMethod , which allows them to examine the exact method, its parameters and
associated annotations. The processing for a URL no longer needs to be split across
different controllers.
There are also several things no longer possible:
-
Select a controller first with a
SimpleUrlHandlerMapping or
BeanNameUrlHandlerMapping and then narrow the method based on @RequestMapping
annotations.
-
Rely on method names as a fall-back mechanism to disambiguate between two
@RequestMapping methods that don’t have an explicit path mapping URL path but
otherwise match equally, e.g. by HTTP method. In the new support classes
@RequestMapping methods have to be mapped uniquely.
-
Have a single default method (without an explicit path mapping) with which requests
are processed if no other controller method matches more concretely. In the new
support classes if a matching method is not found a 404 error is raised.
The above features are still supported with the existing support classes. However to
take advantage of new Spring MVC 3.1 features you’ll need to use the new support classes.
URI templates can be used for convenient access to selected parts of a URL in a
@RequestMapping method.
A URI Template is a URI-like string, containing one or more variable names. When you
substitute values for these variables, the template becomes a URI. The
proposed RFC for URI Templates defines
how a URI is parameterized. For example, the URI Template
http://www.example.com/users/{userId} contains the variable userId. Assigning the
value fred to the variable yields http://www.example.com/users/fred .
In Spring MVC you can use the @PathVariable annotation on a method argument to bind it
to the value of a URI template variable:
@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(@PathVariable String ownerId, Model model) {
Owner owner = ownerService.findOwner(ownerId);
model.addAttribute("owner", owner);
return "displayOwner";
}
The URI Template " /owners/{ownerId} " specifies the variable name ownerId . When the
controller handles this request, the value of ownerId is set to the value found in the
appropriate part of the URI. For example, when a request comes in for /owners/fred ,
the value of ownerId is fred .
![[Tip]](images/tip.png) | Tip |
---|
To process the @PathVariable annotation, Spring MVC needs to find the matching URI
template variable by name. You can specify it in the annotation:
@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(@PathVariable("ownerId") String theOwner, Model model) {
}
Or if the URI template variable name matches the method argument name you can omit that
detail. As long as your code is not compiled without debugging information, Spring MVC
will match the method argument name to the URI template variable name:
@RequestMapping(value="/owners/{ownerId}", method=RequestMethod.GET)
public String findOwner(@PathVariable String ownerId, Model model) {
}
|
A method can have any number of @PathVariable annotations:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET)
public String findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
Owner owner = ownerService.findOwner(ownerId);
Pet pet = owner.getPet(petId);
model.addAttribute("pet", pet);
return "displayPet";
}
When a @PathVariable annotation is used on a Map<String, String> argument, the map
is populated with all URI template variables.
A URI template can be assembled from type and path level @RequestMapping
annotations. As a result the findPet() method can be invoked with a URL such as
/owners/42/pets/21 .
@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {
@RequestMapping("/pets/{petId}")
public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
}
}
A @PathVariable argument can be of any simple type such as int, long, Date, etc.
Spring automatically converts to the appropriate type or throws a
TypeMismatchException if it fails to do so. You can also register support for parsing
additional data types. See the section called “Method Parameters And Type Conversion” and the section called “Customizing WebDataBinder initialization”.
URI Template Patterns with Regular Expressions
Sometimes you need more precision in defining URI template variables. Consider the URL
"/spring-web/spring-web-3.0.5.jar" . How do you break it down into multiple parts?
The @RequestMapping annotation supports the use of regular expressions in URI template
variables. The syntax is {varName:regex} where the first part defines the variable
name and the second - the regular expression.For example:
@RequestMapping("/spring-web/{symbolicName:[a-z-]}-{version:\\d\\.\\d\\.\\d}{extension:\\.[a-z] }")
public void handle(@PathVariable String version, @PathVariable String extension) {
}
}
In addition to URI templates, the @RequestMapping annotation also supports Ant-style
path patterns (for example, /myPath/*.do ). A combination of URI template variables and
Ant-style globs is also supported (e.g. /owners/*/pets/{petId} ).
Patterns with Placeholders
Patterns in @RequestMapping annotations support ${…} placeholders against local
properties and/or system properties and environment variables. This may be useful in
cases where the path a controller is mapped to may need to be customized through
configuration. For more information on placeholders, see the javadocs of the
PropertyPlaceholderConfigurer class.
The URI specification RFC 3986 defines
the possibility of including name-value pairs within path segments. There is no specific
term used in the spec. The general "URI path parameters" could be applied although the
more unique "Matrix URIs", originating
from an old post by Tim Berners-Lee, is also frequently used and fairly well known.
Within Spring MVC these are referred to as matrix variables.
Matrix variables can appear in any path segment, each matrix variable separated with a
";" (semicolon). For example: "/cars;color=red;year=2012" . Multiple values may be
either "," (comma) separated "color=red,green,blue" or the variable name may be
repeated "color=red;color=green;color=blue" .
If a URL is expected to contain matrix variables, the request mapping pattern must
represent them with a URI template. This ensures the request can be matched correctly
regardless of whether matrix variables are present or not and in what order they are
provided.
Below is an example of extracting the matrix variable "q":
@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET)
public void findPet(@PathVariable String petId, @MatrixVariable int q) {
}
Since all path segments may contain matrix variables, in some cases you need to be more
specific to identify where the variable is expected to be:
@RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET)
public void findPet(
@MatrixVariable(value="q", pathVar="ownerId") int q1,
@MatrixVariable(value="q", pathVar="petId") int q2) {
}
A matrix variable may be defined as optional and a default value specified:
@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET)
public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) {
}
All matrix variables may be obtained in a Map:
@RequestMapping(value = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET)
public void findPet(
@MatrixVariable Map<String, String> matrixVars,
@MatrixVariable(pathVar="petId"") Map<String, String> petMatrixVars) {
}
Note that to enable the use of matrix variables, you must set the
removeSemicolonContent property of RequestMappingHandlerMapping to false . By
default it is set to true .
![[Tip]](images/tip.png) | Tip |
---|
The MVC Java config and the MVC namespace both provide options for enabling the use of
matrix variables.
If you are using Java config, The Advanced Customizations
with MVC Java Config section describes how the RequestMappingHandlerMapping can
be customized.
In the MVC namespace, the <mvc:annotation-driven> element has an
enable-matrix-variables attribute that should be set to true . By default it is set
to false .
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<mvc:annotation-driven enable-matrix-variables="true"/>
</beans>
|
You can narrow the primary mapping by specifying a list of consumable media types. The
request will be matched only if the Content-Type request header matches the specified
media type. For example:
@Controller
@RequestMapping(value = "/pets", method = RequestMethod.POST, consumes="application/json")
public void addPet(@RequestBody Pet pet, Model model) {
}
Consumable media type expressions can also be negated as in !text/plain to match to
all requests other than those with Content-Type of text/plain.
![[Tip]](images/tip.png) | Tip |
---|
The consumes condition is supported on the type and on the method level. Unlike most
other conditions, when used at the type level, method-level consumable types override
rather than extend type-level consumable types.
|
You can narrow the primary mapping by specifying a list of producible media types. The
request will be matched only if the Accept request header matches one of these
values. Furthermore, use of the produces condition ensures the actual content type
used to generate the response respects the media types specified in the produces
condition. For example:
@Controller
@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, produces="application/json")
@ResponseBody
public Pet getPet(@PathVariable String petId, Model model) {
}
Just like with consumes, producible media type expressions can be negated as in
!text/plain to match to all requests other than those with an Accept header
value of text/plain.
![[Tip]](images/tip.png) | Tip |
---|
The produces condition is supported on the type and on the method level. Unlike most
other conditions, when used at the type level, method-level producible types override
rather than extend type-level producible types.
|
Request Parameters and Header Values
You can narrow request matching through request parameter conditions such as
"myParam" , "!myParam" , or "myParam=myValue" . The first two test for request
parameter presence/absence and the third for a specific parameter value. Here is an
example with a request parameter value condition:
@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {
@RequestMapping(value = "/pets/{petId}", method = RequestMethod.GET, params="myParam=myValue")
public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
}
}
The same can be done to test for request header presence/absence or to match based on a
specific request header value:
@Controller
@RequestMapping("/owners/{ownerId}")
public class RelativePathUriTemplateController {
@RequestMapping(value = "/pets", method = RequestMethod.GET, headers="myHeader=myValue")
public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) {
}
}
![[Tip]](images/tip.png) | Tip |
---|
Although you can match to Content-Type and Accept header values using media type
wild cards (for example "content-type=text/*" will match to "text/plain" and
"text/html"), it is recommended to use the consumes and produces conditions
respectively instead. They are intended specifically for that purpose.
|
16.3.3 Defining @RequestMapping handler methods
An @RequestMapping handler method can have a very flexible signatures. The supported
method arguments and return values are described in the following section. Most
arguments can be used in arbitrary order with the only exception of BindingResult
arguments. This is described in the next section.
![[Note]](images/note.png) | Note |
---|
Spring 3.1 introduced a new set of support classes for @RequestMapping methods called
RequestMappingHandlerMapping and RequestMappingHandlerAdapter respectively. They are
recommended for use and even required to take advantage of new features in Spring MVC
3.1 and going forward. The new support classes are enabled by default from the MVC
namespace and with use of the MVC Java config but must be configured explicitly if using
neither.
|
Supported method argument types
The following are the supported method arguments:
-
Request or response objects (Servlet API). Choose any specific request or response
type, for example
ServletRequest or HttpServletRequest .
-
Session object (Servlet API): of type
HttpSession . An argument of this type enforces
the presence of a corresponding session. As a consequence, such an argument is never
null .
![[Note]](images/note.png) | Note |
---|
Session access may not be thread-safe, in particular in a Servlet environment. Consider
setting the RequestMappingHandlerAdapter 's "synchronizeOnSession" flag to "true" if
multiple requests are allowed to access a session concurrently.
|
-
org.springframework.web.context.request.WebRequest or
org.springframework.web.context.request.NativeWebRequest . Allows for generic
request parameter access as well as request/session attribute access, without ties
to the native Servlet/Portlet API.
-
java.util.Locale for the current request locale, determined by the most specific
locale resolver available, in effect, the configured LocaleResolver /
LocaleContextResolver in an MVC environment.
-
java.util.TimeZone (Java 6+) / java.time.ZoneId (on Java 8) for the time zone
associated with the current request, as determined by a LocaleContextResolver .
-
java.io.InputStream / java.io.Reader for access to the request’s content.
This value is the raw InputStream/Reader as exposed by the Servlet API.
-
java.io.OutputStream / java.io.Writer for generating the response’s content.
This value is the raw OutputStream/Writer as exposed by the Servlet API.
-
org.springframework.http.HttpMethod for the HTTP request method.
-
java.security.Principal containing the currently authenticated user.
-
@PathVariable annotated parameters for access to URI template variables. See
the section called “URI Template Patterns”.
-
@MatrixVariable annotated parameters for access to name-value pairs located in
URI path segments. See the section called “Matrix Variables”.
-
@RequestParam annotated parameters for access to specific Servlet request
parameters. Parameter values are converted to the declared method argument type.
See the section called “Binding request parameters to method parameters with @RequestParam”.
-
@RequestHeader annotated parameters for access to specific Servlet request HTTP
headers. Parameter values are converted to the declared method argument type.
-
@RequestBody annotated parameters for access to the HTTP request body. Parameter
values are converted to the declared method argument type using
HttpMessageConverter s. See the section called “Mapping the request body with the @RequestBody annotation”.
-
@RequestPart annotated parameters for access to the content of a
"multipart/form-data" request part. See Section 16.11.5, “Handling a file upload request from programmatic clients” and
Section 16.11, “Spring’s multipart (file upload) support”.
-
HttpEntity<?> parameters for access to the Servlet request HTTP headers and
contents. The request stream will be converted to the entity body using
HttpMessageConverter s. See the section called “Using HttpEntity”.
-
java.util.Map / org.springframework.ui.Model / org.springframework.ui.ModelMap
for enriching the implicit model that is exposed to the web view.
-
org.springframework.web.servlet.mvc.support.RedirectAttributes to specify the exact
set of attributes to use in case of a redirect and also to add flash attributes
(attributes stored temporarily on the server-side to make them available to the
request after the redirect). RedirectAttributes is used instead of the implicit
model if the method returns a "redirect:" prefixed view name or RedirectView .
-
Command or form objects to bind request parameters to bean properties (via setters)
or directly to fields, with customizable type conversion, depending on
@InitBinder
methods and/or the HandlerAdapter configuration. See the webBindingInitializer
property on RequestMappingHandlerAdapter . Such command objects along with their
validation results will be exposed as model attributes by default, using the command
class class name - e.g. model attribute "orderAddress" for a command object of type
"some.package.OrderAddress". The ModelAttribute annotation can be used on a method
argument to customize the model attribute name used.
-
org.springframework.validation.Errors /
org.springframework.validation.BindingResult validation results for a preceding
command or form object (the immediately preceding method argument).
-
org.springframework.web.bind.support.SessionStatus status handle for marking form
processing as complete, which triggers the cleanup of session attributes that have
been indicated by the @SessionAttributes annotation at the handler type level.
-
org.springframework.web.util.UriComponentsBuilder a builder for preparing a URL
relative to the current request’s host, port, scheme, context path, and the literal
part of the servlet mapping.
The Errors or BindingResult parameters have to follow the model object that is being
bound immediately as the method signature might have more that one model object and
Spring will create a separate BindingResult instance for each of them so the following
sample won’t work:
Invalid ordering of BindingResult and @ModelAttribute.
@RequestMapping(method = RequestMethod.POST)
public String processSubmit(@ModelAttribute("pet") Pet pet, Model model, BindingResult result) { ... }
Note, that there is a Model parameter in between Pet and BindingResult . To get
this working you have to reorder the parameters as follows:
@RequestMapping(method = RequestMethod.POST)
public String processSubmit(**@ModelAttribute("pet") Pet pet**, **BindingResult result**, Model model) { ... }
Supported method return types
The following are the supported return types:
-
A
ModelAndView object, with the model implicitly enriched with command objects and
the results of @ModelAttribute annotated reference data accessor methods.
-
A
Model object, with the view name implicitly determined through a
RequestToViewNameTranslator and the model implicitly enriched with command objects
and the results of @ModelAttribute annotated reference data accessor methods.
-
A
Map object for exposing a model, with the view name implicitly determined through
a RequestToViewNameTranslator and the model implicitly enriched with command objects
and the results of @ModelAttribute annotated reference data accessor methods.
-
A
View object, with the model implicitly determined through command objects and
@ModelAttribute annotated reference data accessor methods. The handler method may
also programmatically enrich the model by declaring a Model argument (see above).
-
A
String value that is interpreted as the logical view name, with the model
implicitly determined through command objects and @ModelAttribute annotated
reference data accessor methods. The handler method may also programmatically enrich
the model by declaring a Model argument (see above).
-
void if the method handles the response itself (by writing the response content
directly, declaring an argument of type ServletResponse / HttpServletResponse for
that purpose) or if the view name is supposed to be implicitly determined through a
RequestToViewNameTranslator (not declaring a response argument in the handler method
signature).
-
If the method is annotated with
@ResponseBody , the return type is written to the
response HTTP body. The return value will be converted to the declared method argument
type using HttpMessageConverter s. See the section called “Mapping the response body with the @ResponseBody annotation”.
-
An
HttpEntity<?> or ResponseEntity<?> object to provide access to the Servlet
response HTTP headers and contents. The entity body will be converted to the response
stream using HttpMessageConverter s. See the section called “Using HttpEntity”.
-
An
HttpHeaders object to return a response with no body.
-
A
Callable<?> can be returned when the application wants to produce the return value
asynchronously in a thread managed by Spring MVC.
-
A
DeferredResult<?> can be returned when the application wants to produce the return
value from a thread of its own choosing.
-
Any other return type is considered to be a single model attribute to be exposed to
the view, using the attribute name specified through
@ModelAttribute at the method
level (or the default attribute name based on the return type class name). The model
is implicitly enriched with command objects and the results of @ModelAttribute
annotated reference data accessor methods.
Binding request parameters to method parameters with @RequestParam
Use the @RequestParam annotation to bind request parameters to a method parameter in
your controller.
The following code snippet shows the usage:
@Controller
@RequestMapping("/pets")
@SessionAttributes("pet")
public class EditPetForm {
@RequestMapping(method = RequestMethod.GET)
public String setupForm(**@RequestParam("petId") int petId**, ModelMap model) {
Pet pet = this.clinic.loadPet(petId);
model.addAttribute("pet", pet);
return "petForm";
}
}
Parameters using this annotation are required by default, but you can specify that a
parameter is optional by setting @RequestParam 's required attribute to false
(e.g., @RequestParam(value="id", required=false) ).
Type conversion is applied automatically if the target method parameter type is not
String . See the section called “Method Parameters And Type Conversion”.
Mapping the request body with the @RequestBody annotation
The @RequestBody method parameter annotation indicates that a method parameter should
be bound to the value of the HTTP request body. For example:
@RequestMapping(value = "/something", method = RequestMethod.PUT)
public void handle(@RequestBody String body, Writer writer) throws IOException {
writer.write(body);
}
You convert the request body to the method argument by using an HttpMessageConverter .
HttpMessageConverter is responsible for converting from the HTTP request message to an
object and converting from an object to the HTTP response body. The
RequestMappingHandlerAdapter supports the @RequestBody annotation with the following
default HttpMessageConverters :
-
ByteArrayHttpMessageConverter converts byte arrays.
-
StringHttpMessageConverter converts strings.
-
FormHttpMessageConverter converts form data to/from a MultiValueMap<String, String>.
-
SourceHttpMessageConverter converts to/from a javax.xml.transform.Source.
For more information on these converters, see Message
Converters. Also note that if using the MVC namespace or the MVC Java config, a wider
range of message converters are registered by default. See Section 16.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” for more information.
If you intend to read and write XML, you will need to configure the
MarshallingHttpMessageConverter with a specific Marshaller and an Unmarshaller
implementation from the org.springframework.oxm package. The example below shows how
to do that directly in your configuration but if your application is configured through
the MVC namespace or the MVC Java config see Section 16.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” instead.
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
<property name="messageConverters">
<util:list id="beanList">
<ref bean="stringHttpMessageConverter"/>
<ref bean="marshallingHttpMessageConverter"/>
</util:list>
</property
</bean>
<bean id="stringHttpMessageConverter"
class="org.springframework.http.converter.StringHttpMessageConverter"/>
<bean id="marshallingHttpMessageConverter"
class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
<property name="marshaller" ref="castorMarshaller" />
<property name="unmarshaller" ref="castorMarshaller" />
</bean>
<bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/>
An @RequestBody method parameter can be annotated with @Valid , in which case it will
be validated using the configured Validator instance. When using the MVC namespace or
the MVC Java config, a JSR-303 validator is configured automatically assuming a JSR-303
implementation is available on the classpath.
Just like with @ModelAttribute parameters, an Errors argument can be used to examine
the errors. If such an argument is not declared, a MethodArgumentNotValidException
will be raised. The exception is handled in the DefaultHandlerExceptionResolver , which
sends a 400 error back to the client.
Mapping the response body with the @ResponseBody annotation
The @ResponseBody annotation is similar to @RequestBody . This annotation can be put
on a method and indicates that the return type should be written straight to the HTTP
response body (and not placed in a Model, or interpreted as a view name). For example:
@RequestMapping(value = "/something", method = RequestMethod.PUT)
@ResponseBody
public String helloWorld() {
return "Hello World";
}
The above example will result in the text Hello World being written to the HTTP
response stream.
As with @RequestBody , Spring converts the returned object to a response body by using
an HttpMessageConverter . For more information on these converters, see the previous
section and Message Converters.
Creating REST Controllers with the @RestController annotation
It’s a very common use case to have Controllers implement a REST API, thus serving only
JSON, XML or custom MediaType content. For convenience, instead of annotating all your
@RequestMapping methods with @ResponseBody , you can annotate your Controller Class
with @RestController .
@RestController
is a stereotype annotation that combines @ResponseBody and @Controller . More than
that, it gives more meaning to your Controller and also may carry additional semantics
in future releases of the framework.
As with regular @Controller s, a @RestController may be assisted by a
@ControllerAdvice Bean. See the the section called “Advising controllers with the @ControllerAdvice annotation” section for more details.
The HttpEntity is similar to @RequestBody and @ResponseBody . Besides getting
access to the request and response body, HttpEntity (and the response-specific
subclass ResponseEntity ) also allows access to the request and response headers, like
so:
@RequestMapping("/something")
public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws UnsupportedEncodingException {
String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader"));
byte[] requestBody = requestEntity.getBody();
HttpHeaders responseHeaders = new HttpHeaders();
responseHeaders.set("MyResponseHeader", "MyValue");
return new ResponseEntity<String>("Hello World", responseHeaders, HttpStatus.CREATED);
}
The above example gets the value of the MyRequestHeader request header, and reads the
body as a byte array. It adds the MyResponseHeader to the response, writes Hello
World to the response stream, and sets the response status code to 201 (Created).
As with @RequestBody and @ResponseBody , Spring uses HttpMessageConverter to
convert from and to the request and response streams. For more information on these
converters, see the previous section and Message Converters.
Using @ModelAttribute on a method
The @ModelAttribute annotation can be used on methods or on method arguments. This
section explains its usage on methods while the next section explains its usage on
method arguments.
An @ModelAttribute on a method indicates the purpose of that method is to add one or
more model attributes. Such methods support the same argument types as @RequestMapping
methods but cannot be mapped directly to requests. Instead @ModelAttribute methods in
a controller are invoked before @RequestMapping methods, within the same controller. A
couple of examples:
@ModelAttribute
public Account addAccount(@RequestParam String number) {
return accountManager.findAccount(number);
}
@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
model.addAttribute(accountManager.findAccount(number));
}
@ModelAttribute methods are used to populate the model with commonly needed attributes
for example to fill a drop-down with states or with pet types, or to retrieve a command
object like Account in order to use it to represent the data on an HTML form. The latter
case is further discussed in the next section.
Note the two styles of @ModelAttribute methods. In the first, the method adds an
attribute implicitly by returning it. In the second, the method accepts a Model and
adds any number of model attributes to it. You can choose between the two styles
depending on your needs.
A controller can have any number of @ModelAttribute methods. All such methods are
invoked before @RequestMapping methods of the same controller.
@ModelAttribute methods can also be defined in an @ControllerAdvice -annotated class
and such methods apply to many controllers. See the the section called “Advising controllers with the @ControllerAdvice annotation” section
for more details.
![[Tip]](images/tip.png) | Tip |
---|
What happens when a model attribute name is not explicitly specified? In such cases a
default name is assigned to the model attribute based on its type. For example if the
method returns an object of type Account , the default name used is "account". You can
change that through the value of the @ModelAttribute annotation. If adding attributes
directly to the Model , use the appropriate overloaded addAttribute(..) method -
i.e., with or without an attribute name.
|
The @ModelAttribute annotation can be used on @RequestMapping methods as well. In
that case the return value of the @RequestMapping method is interpreted as a model
attribute rather than as a view name. The view name is derived from view name
conventions instead much like for methods returning void — see Section 16.13.3, “The View - RequestToViewNameTranslator”.
Using @ModelAttribute on a method argument
As explained in the previous section @ModelAttribute can be used on methods or on
method arguments. This section explains its usage on method arguments.
An @ModelAttribute on a method argument indicates the argument should be retrieved
from the model. If not present in the model, the argument should be instantiated first
and then added to the model. Once present in the model, the argument’s fields should be
populated from all request parameters that have matching names. This is known as data
binding in Spring MVC, a very useful mechanism that saves you from having to parse each
form field individually.
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@ModelAttribute Pet pet) { }
Given the above example where can the Pet instance come from? There are several options:
An @ModelAttribute method is a common way to to retrieve an attribute from the
database, which may optionally be stored between requests through the use of
@SessionAttributes . In some cases it may be convenient to retrieve the attribute by
using an URI template variable and a type converter. Here is an example:
@RequestMapping(value="/accounts/{account}", method = RequestMethod.PUT)
public String save(@ModelAttribute("account") Account account) {
}
In this example the name of the model attribute (i.e. "account") matches the name of a
URI template variable. If you register Converter<String, Account> that can turn the
String account value into an Account instance, then the above example will work
without the need for an @ModelAttribute method.
The next step is data binding. The WebDataBinder class matches request parameter names — including query string parameters and form fields — to model attribute fields by
name. Matching fields are populated after type conversion (from String to the target
field type) has been applied where necessary. Data binding and validation are covered in
Chapter 6, Validation, Data Binding, and Type Conversion. Customizing the data binding process for a controller level is covered
in the section called “Customizing WebDataBinder initialization”.
As a result of data binding there may be errors such as missing required fields or type
conversion errors. To check for such errors add a BindingResult argument immediately
following the @ModelAttribute argument:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {
if (result.hasErrors()) {
return "petForm";
}
}
With a BindingResult you can check if errors were found in which case it’s common to
render the same form where the errors can be shown with the help of Spring’s <errors>
form tag.
In addition to data binding you can also invoke validation using your own custom
validator passing the same BindingResult that was used to record data binding errors.
That allows for data binding and validation errors to be accumulated in one place and
subsequently reported back to the user:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {
new PetValidator().validate(pet, result);
if (result.hasErrors()) {
return "petForm";
}
}
Or you can have validation invoked automatically by adding the JSR-303 @Valid
annotation:
@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST)
public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) {
if (result.hasErrors()) {
return "petForm";
}
}
See Section 6.8, “Spring Validation” and Chapter 6, Validation, Data Binding, and Type Conversion for details on how to configure and
use validation.
Using @SessionAttributes to store model attributes in the HTTP session between requests
The type-level @SessionAttributes annotation declares session attributes used by a
specific handler. This will typically list the names of model attributes or types of
model attributes which should be transparently stored in the session or some
conversational storage, serving as form-backing beans between subsequent requests.
The following code snippet shows the usage of this annotation, specifying the model
attribute name:
@Controller
@RequestMapping("/editPet.do")
@SessionAttributes("pet")
public class EditPetForm {
}
Specifying redirect and flash attributes
By default all model attributes are considered to be exposed as URI template variables
in the redirect URL. Of the remaining attributes those that are primitive types or
collections/arrays of primitive types are automatically appended as query parameters.
In annotated controllers however the model may contain additional attributes originally
added for rendering purposes (e.g. drop-down field values). To gain precise control over
the attributes used in a redirect scenario, an @RequestMapping method can declare an
argument of type RedirectAttributes and use it to add attributes for use in
RedirectView . If the controller method does redirect, the content of
RedirectAttributes is used. Otherwise the content of the default Model is used.
The RequestMappingHandlerAdapter provides a flag called
"ignoreDefaultModelOnRedirect" that can be used to indicate the content of the default
Model should never be used if a controller method redirects. Instead the controller
method should declare an attribute of type RedirectAttributes or if it doesn’t do so
no attributes should be passed on to RedirectView . Both the MVC namespace and the MVC
Java config keep this flag set to false in order to maintain backwards compatibility.
However, for new applications we recommend setting it to true
The RedirectAttributes interface can also be used to add flash attributes. Unlike
other redirect attributes, which end up in the target redirect URL, flash attributes are
saved in the HTTP session (and hence do not appear in the URL). The model of the
controller serving the target redirect URL automatically receives these flash attributes
after which they are removed from the session. See Section 16.6, “Using flash attributes” for an
overview of the general support for flash attributes in Spring MVC.
Working with "application/x-www-form-urlencoded" data
The previous sections covered use of @ModelAttribute to support form submission
requests from browser clients. The same annotation is recommended for use with requests
from non-browser clients as well. However there is one notable difference when it comes
to working with HTTP PUT requests. Browsers can submit form data via HTTP GET or HTTP
POST. Non-browser clients can also submit forms via HTTP PUT. This presents a challenge
because the Servlet specification requires the ServletRequest.getParameter*() family
of methods to support form field access only for HTTP POST, not for HTTP PUT.
To support HTTP PUT and PATCH requests, the spring-web module provides the filter
HttpPutFormContentFilter , which can be configured in web.xml :
<filter>
<filter-name>httpPutFormFilter</filter-name>
<filter-class>org.springframework.web.filter.HttpPutFormContentFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>httpPutFormFilter</filter-name>
<servlet-name>dispatcherServlet</servlet-name>
</filter-mapping>
<servlet>
<servlet-name>dispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
</servlet>
The above filter intercepts HTTP PUT and PATCH requests with content type
application/x-www-form-urlencoded , reads the form data from the body of the request,
and wraps the ServletRequest in order to make the form data available through the
ServletRequest.getParameter*() family of methods.
![[Note]](images/note.png) | Note |
---|
As HttpPutFormContentFilter consumes the body of the request, it should not be
configured for PUT or PATCH URLs that rely on other converters for
application/x-www-form-urlencoded . This includes @RequestBody MultiValueMap<String,
String> and HttpEntity<MultiValueMap<String, String>> .
|
Mapping cookie values with the @CookieValue annotation
The @CookieValue annotation allows a method parameter to be bound to the value of an
HTTP cookie.
Let us consider that the following cookie has been received with an http request:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
The following code sample demonstrates how to get the value of the JSESSIONID cookie:
@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) {
}
Type conversion is applied automatically if the target method parameter type is not
String . See the section called “Method Parameters And Type Conversion”.
This annotation is supported for annotated handler methods in Servlet and Portlet
environments.
Mapping request header attributes with the @RequestHeader annotation
The @RequestHeader annotation allows a method parameter to be bound to a request header.
Here is a sample request header:
Host localhost:8080
Accept text/html,application/xhtml+xml,application/xml;q=0.9
Accept-Language fr,en-gb;q=0.7,en;q=0.3
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300
The following code sample demonstrates how to get the value of the Accept-Encoding and
Keep-Alive headers:
@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding,
@RequestHeader("Keep-Alive") long keepAlive) {
}
Type conversion is applied automatically if the method parameter is not String . See
the section called “Method Parameters And Type Conversion”.
![[Tip]](images/tip.png) | Tip |
---|
Built-in support is available for converting a comma-separated string into an
array/collection of strings or other types known to the type conversion system. For
example a method parameter annotated with @RequestHeader("Accept") may be of type
String but also String[] or List<String> .
|
This annotation is supported for annotated handler methods in Servlet and Portlet
environments.
Method Parameters And Type Conversion
String-based values extracted from the request including request parameters, path
variables, request headers, and cookie values may need to be converted to the target
type of the method parameter or field (e.g., binding a request parameter to a field in
an @ModelAttribute parameter) they’re bound to. If the target type is not String ,
Spring automatically converts to the appropriate type. All simple types such as int,
long, Date, etc. are supported. You can further customize the conversion process through
a WebDataBinder (see the section called “Customizing WebDataBinder initialization”) or by registering Formatters with
the FormattingConversionService (see Section 6.6, “Spring Field Formatting”).
Customizing WebDataBinder initialization
To customize request parameter binding with PropertyEditors through Spring’s
WebDataBinder , you can use @InitBinder -annotated methods within your controller,
@InitBinder methods within an @ControllerAdvice class, or provide a custom
WebBindingInitializer . See the the section called “Advising controllers with the @ControllerAdvice annotation” section for more details.
Customizing data binding with @InitBinder
Annotating controller methods with @InitBinder allows you to configure web data
binding directly within your controller class. @InitBinder identifies methods that
initialize the WebDataBinder that will be used to populate command and form object
arguments of annotated handler methods.
Such init-binder methods support all arguments that @RequestMapping supports, except
for command/form objects and corresponding validation result objects. Init-binder
methods must not have a return value. Thus, they are usually declared as void . Typical
arguments include WebDataBinder in combination with WebRequest or
java.util.Locale , allowing code to register context-specific editors.
The following example demonstrates the use of @InitBinder to configure a
CustomDateEditor for all java.util.Date form properties.
@Controller
public class MyFormController {
@InitBinder
public void initBinder(WebDataBinder binder) {
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
dateFormat.setLenient(false);
binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
}
}
Configuring a custom WebBindingInitializer
To externalize data binding initialization, you can provide a custom implementation of
the WebBindingInitializer interface, which you then enable by supplying a custom bean
configuration for an AnnotationMethodHandlerAdapter , thus overriding the default
configuration.
The following example from the PetClinic application shows a configuration using a
custom implementation of the WebBindingInitializer interface,
org.springframework.samples.petclinic.web.ClinicBindingInitializer , which configures
PropertyEditors required by several of the PetClinic controllers.
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
<property name="cacheSeconds" value="0" />
<property name="webBindingInitializer">
<bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" />
</property>
</bean>
@InitBinder methods can also be defined in an @ControllerAdvice -annotated class in
which case they apply to matching controllers. This provides an alternative to using a
WebBindingInitializer . See the the section called “Advising controllers with the @ControllerAdvice annotation” section for more details.
Support for the Last-Modified Response Header To Facilitate Content Caching
An @RequestMapping method may wish to support 'Last-Modified' HTTP requests, as
defined in the contract for the Servlet API’s getLastModified method, to facilitate
content caching. This involves calculating a lastModified long value for a given
request, comparing it against the 'If-Modified-Since' request header value, and
potentially returning a response with status code 304 (Not Modified). An annotated
controller method can achieve that as follows:
@RequestMapping
public String myHandleMethod(WebRequest webRequest, Model model) {
long lastModified =
if (request.checkNotModified(lastModified)) {
return null;
}
model.addAttribute(...);
return "myViewName";
}
There are two key elements to note: calling request.checkNotModified(lastModified) and
returning null . The former sets the response status to 304 before it returns true .
The latter, in combination with the former, causes Spring MVC to do no further
processing of the request.
Advising controllers with the @ControllerAdvice annotation
The @ControllerAdvice annotation is a component annotation allowing implementation
classes to be auto-detected through classpath scanning. It is automatically enabled when
using the MVC namespace or the MVC Java config.
Classes annotated with @ControllerAdvice can contain @ExceptionHandler ,
@InitBinder , and @ModelAttribute annotated methods, and these methods will apply to
@RequestMapping methods across all controller hierarchies as opposed to the controller
hierarchy within which they are declared.
The @ControllerAdvice annotation can also target a subset of controllers with its
attributes:
@ControllerAdvice(annotations = RestController.class)
public class AnnotationAdvice {}
@ControllerAdvice("org.example.controllers")
public class BasePackageAdvice {}
@ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class})
public class AssignableTypesAdvice {}
Check out the
@ControllerAdvice
documentation for more details.
16.3.4 Asynchronous Request Processing
Spring MVC 3.2 introduced Servlet 3 based asynchronous request processing. Instead of
returning a value, as usual, a controller method can now return a
java.util.concurrent.Callable and produce the return value from a separate thread.
Meanwhile the main Servlet container thread is released and allowed to process other
requests. Spring MVC invokes the Callable in a separate thread with the help of a
TaskExecutor and when the Callable returns, the request is dispatched back to the
Servlet container to resume processing with the value returned by the Callable . Here
is an example controller method:
@RequestMapping(method=RequestMethod.POST)
public Callable<String> processUpload(final MultipartFile file) {
return new Callable<String>() {
public String call() throws Exception {
return "someView";
}
};
}
A second option is for the controller to return an instance of DeferredResult . In this
case the return value will also be produced from a separate thread. However, that thread
is not known to Spring MVC. For example the result may be produced in response to some
external event such as a JMS message, a scheduled task, etc. Here is an example
controller method:
@RequestMapping("/quotes")
@ResponseBody
public DeferredResult<String> quotes() {
DeferredResult<String> deferredResult = new DeferredResult<String>();
return deferredResult;
}
deferredResult.setResult(data);
This may be difficult to understand without any knowledge of the Servlet 3 async
processing feature. It would certainly help to read up on it. At a very minimum consider
the following basic facts:
-
A
ServletRequest can be put in asynchronous mode by calling request.startAsync() .
The main effect of doing so is that the Servlet, as well as any Filters, can exit but
the response will remain open allowing some other thread to complete processing.
-
The call to
request.startAsync() returns an AsyncContext , which can be used for
further control over async processing. For example it provides the method dispatch ,
which can be called from an application thread in order to "dispatch" the request back
to the Servlet container. An async dispatch is similar to a forward except it is made
from one (application) thread to another (Servlet container) thread whereas a forward
occurs synchronously in the same (Servlet container) thread.
-
ServletRequest provides access to the current DispatcherType , which can be used to
distinguish if a Servlet or a Filter is processing on the initial request
processing thread and when it is processing in an async dispatch.
With the above in mind, the following is the sequence of events for async request
processing with a Callable : (1) Controller returns a Callable , (2) Spring MVC starts
async processing and submits the Callable to a TaskExecutor for processing in a
separate thread, (3) the DispatcherServlet and all Filter’s exit the request
processing thread but the response remains open, (4) the Callable produces a result
and Spring MVC dispatches the request back to the Servlet container, (5) the
DispatcherServlet is invoked again and processing resumes with the asynchronously
produced result from the Callable . The exact sequencing of (2), (3), and (4) may vary
depending on the speed of execution of the concurrent threads.
The sequence of events for async request processing with a DeferredResult is the same
in principal except it’s up to the application to produce the asynchronous result from
some thread: (1) Controller returns a DeferredResult and saves it in some in-memory
queue or list where it can be accessed, (2) Spring MVC starts async processing, (3) the
DispatcherServlet and all configured Filter’s exit the request processing thread but
the response remains open, (4) the application sets the DeferredResult from some
thread and Spring MVC dispatches the request back to the Servlet container, (5) the
DispatcherServlet is invoked again and processing resumes with the asynchronously
produced result.
Explaining the motivation for async request processing and when or why to use it are
beyond the scope of this document. For further information you may wish to read
this
blog post series.
Exception Handling for Async Requests
What happens if a Callable returned from a controller method raises an Exception while
being executed? The effect is similar to what happens when any controller method raises
an exception. It is handled by a matching @ExceptionHandler method in the same
controller or by one of the configured HandlerExceptionResolver instances.
![[Note]](images/note.png) | Note |
---|
Under the covers, when a Callable raises an Exception, Spring MVC still dispatches to
the Servlet container to resume processing. The only difference is that the result of
executing the Callable is an Exception that must be processed with the configured
HandlerExceptionResolver instances.
|
When using a DeferredResult , you have a choice of calling its setErrorResult(Object)
method and provide an Exception or any other Object you’d like to use as the result.
If the result is an Exception , it will be processed with a matching
@ExceptionHandler method in the same controller or with any configured
HandlerExceptionResolver instance.
Intercepting Async Requests
An existing HandlerInterceptor can implement AsyncHandlerInterceptor , which provides
one additional method afterConcurrentHandlingStarted . It is invoked after async
processing starts and when the initial request processing thread is being exited. See
the AsyncHandlerInterceptor javadocs for more details on that.
Further options for async request lifecycle callbacks are provided directly on
DeferredResult , which has the methods onTimeout(Runnable) and
onCompletion(Runnable) . Those are called when the async request is about to time out
or has completed respectively. The timeout event can be handled by setting the
DeferredResult to some value. The completion callback however is final and the result
can no longer be set.
Similar callbacks are also available with a Callable . However, you will need to wrap
the Callable in an instance of WebAsyncTask and then use that to register the
timeout and completion callbacks. Just like with DeferredResult , the timeout event can
be handled and a value can be returned while the completion event is final.
You can also register a CallableProcessingInterceptor or a
DeferredResultProcessingInterceptor globally through the MVC Java config or the MVC
namespace. Those interceptors provide a full set of callbacks and apply every time a
Callable or a DeferredResult is used.
Configuration for Async Request Processing
To use Servlet 3 async request processing, you need to update web.xml to version 3.0:
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0">
...
</web-app>
The DispatcherServlet and any Filter configuration need to have the
<async-supported>true</async-supported> sub-element. Additionally, any Filter that
also needs to get involved in async dispatches should also be configured to support the
ASYNC dispatcher type. Note that it is safe to enable the ASYNC dispatcher type for all
filters provided with the Spring Framework since they will not get involved in async
dispatches unless needed.
![[Warning]](images/warning.png) | Warning |
---|
Note that for some Filters it is absolutely critical to ensure they are mapped to
be invoked during asynchronous dispatches. For example if a filter such as the
OpenEntityManagerInViewFilter is responsible for releasing database connection
resources and must be invoked at the end of an async request.
Below is an example of a propertly configured filter:
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<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0">
<filter>
<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
<filter-class>org.springframework.~.OpenEntityManagerInViewFilter</filter-class>
<async-supported>true</async-supported>
</filter>
<filter-mapping>
<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>ASYNC</dispatcher>
</filter-mapping>
</web-app>
If using Servlet 3, Java based configuration, e.g. via WebApplicationInitializer ,
you’ll also need to set the "asyncSupported" flag as well as the ASYNC dispatcher type
just like with web.xml . To simplify all this configuration, consider extending
AbstractDispatcherServletInitializer or
AbstractAnnotationConfigDispatcherServletInitializer , which automatically set those
options and make it very easy to register Filter instances.
The MVC Java config and the MVC namespace both provide options for configuring async
request processing. WebMvcConfigurer has the method configureAsyncSupport while
<mvc:annotation-driven> has an <async-support> sub-element.
Those allow you to configure the default timeout value to use for async requests, which
if not set depends on the underlying Servlet container (e.g. 10 seconds on Tomcat). You
can also configure an AsyncTaskExecutor to use for executing Callable instances
returned from controller methods. It is highly recommended to configure this property
since by default Spring MVC uses SimpleAsyncTaskExecutor . The MVC Java config and the
MVC namespace also allow you to register CallableProcessingInterceptor and
DeferredResultProcessingInterceptor instances.
If you need to override the default timeout value for a specific DeferredResult , you
can do so by using the appropriate class constructor. Similarly, for a Callable , you
can wrap it in a WebAsyncTask and use the appropriate class constructor to customize
the timeout value. The class constructor of WebAsyncTask also allows providing an
AsyncTaskExecutor .
In previous versions of Spring, users were required to define one or more
HandlerMapping beans in the web application context to map incoming web requests to
appropriate handlers. With the introduction of annotated controllers, you generally
don’t need to do that because the RequestMappingHandlerMapping automatically looks for
@RequestMapping annotations on all @Controller beans. However, do keep in mind that
all HandlerMapping classes extending from AbstractHandlerMapping have the following
properties that you can use to customize their behavior:
-
interceptors List of interceptors to use. HandlerInterceptor s are discussed in
Section 16.4.1, “Intercepting requests with a HandlerInterceptor”.
-
defaultHandler Default handler to use, when this handler mapping does not result in
a matching handler.
-
order Based on the value of the order property (see the
org.springframework.core.Ordered interface), Spring sorts all handler mappings
available in the context and applies the first matching handler.
-
alwaysUseFullPath If true , Spring uses the full path within the current Servlet
context to find an appropriate handler. If false (the default), the path within the
current Servlet mapping is used. For example, if a Servlet is mapped using
/testing/* and the alwaysUseFullPath property is set to true,
/testing/viewPage.php is used, whereas if the property is set to false,
/viewPage.php is used.
-
urlDecode Defaults to true , as of Spring 2.5. If you prefer to compare encoded
paths, set this flag to false . However, the HttpServletRequest always exposes the
Servlet path in decoded form. Be aware that the Servlet path will not match when
compared with encoded paths.
The following example shows how to configure an interceptor:
<beans>
<bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping">
<property name="interceptors">
<bean class="example.MyInterceptor"/>
</property>
</bean>
<beans>
16.4.1 Intercepting requests with a HandlerInterceptor
Spring’s handler mapping mechanism includes handler interceptors, which are useful when
you want to apply specific functionality to certain requests, for example, checking for
a principal.
Interceptors located in the handler mapping must implement HandlerInterceptor from the
org.springframework.web.servlet package. This interface defines three methods:
preHandle(..) is called before the actual handler is executed; postHandle(..) is
called after the handler is executed; and afterCompletion(..) is called after
the complete request has finished. These three methods should provide enough
flexibility to do all kinds of preprocessing and postprocessing.
The preHandle(..) method returns a boolean value. You can use this method to break or
continue the processing of the execution chain. When this method returns true , the
handler execution chain will continue; when it returns false, the DispatcherServlet
assumes the interceptor itself has taken care of requests (and, for example, rendered an
appropriate view) and does not continue executing the other interceptors and the actual
handler in the execution chain.
Interceptors can be configured using the interceptors property, which is present on
all HandlerMapping classes extending from AbstractHandlerMapping . This is shown in
the example below:
<beans>
<bean id="handlerMapping"
class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping">
<property name="interceptors">
<list>
<ref bean="officeHoursInterceptor"/>
</list>
</property>
</bean>
<bean id="officeHoursInterceptor"
class="samples.TimeBasedAccessInterceptor">
<property name="openingTime" value="9"/>
<property name="closingTime" value="18"/>
</bean>
<beans>
package samples;
public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter {
private int openingTime;
private int closingTime;
public void setOpeningTime(int openingTime) {
this.openingTime = openingTime;
}
public void setClosingTime(int closingTime) {
this.closingTime = closingTime;
}
public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
Object handler) throws Exception {
Calendar cal = Calendar.getInstance();
int hour = cal.get(HOUR_OF_DAY);
if (openingTime <= hour && hour < closingTime) {
return true;
}
response.sendRedirect("http://host.com/outsideOfficeHours.php");
return false;
}
}
Any request handled by this mapping is intercepted by the TimeBasedAccessInterceptor .
If the current time is outside office hours, the user is redirected to a static HTML
file that says, for example, you can only access the website during office hours.
![[Note]](images/note.png) | Note |
---|
When using the RequestMappingHandlerMapping the actual handler is an instance of
HandlerMethod which identifies the specific controller method that will be invoked.
|
As you can see, the Spring adapter class HandlerInterceptorAdapter makes it easier to
extend the HandlerInterceptor interface.
![[Tip]](images/tip.png) | Tip |
---|
In the example above, the configured interceptor will apply to all requests handled with
annotated controller methods. If you want to narrow down the URL paths to which an
interceptor applies, you can use the MVC namespace or the MVC Java config, or declare
bean instances of type MappedInterceptor to do that. See Section 16.16.1, “Enabling the MVC Java Config or the MVC XML Namespace”.
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All MVC frameworks for web applications provide a way to address views. Spring provides
view resolvers, which enable you to render models in a browser without tying you to a
specific view technology. Out of the box, Spring enables you to use JSPs, Velocity
templates and XSLT views, for example. See Chapter 17, View technologies for a discussion of how to integrate
and use a number of disparate view technologies.
The two interfaces that are important to the way Spring handles views are ViewResolver
and View . The ViewResolver provides a mapping between view names and actual views.
The View interface addresses the preparation of the request and hands the request over
to one of the view technologies.
16.5.1 Resolving views with the ViewResolver interface
As discussed in Section 16.3, “Implementing Controllers”, all handler methods in the Spring Web MVC
controllers must resolve to a logical view name, either explicitly (e.g., by returning a
String , View , or ModelAndView ) or implicitly (i.e., based on conventions). Views
in Spring are addressed by a logical view name and are resolved by a view resolver.
Spring comes with quite a few view resolvers. This table lists most of them; a couple of
examples follow.
Table 16.3. View resolvers
ViewResolver | Description |
---|
AbstractCachingViewResolver
| Abstract view resolver that caches views. Often views need preparation before they can
be used; extending this view resolver provides caching. | XmlViewResolver
| Implementation of ViewResolver that accepts a configuration file written in XML with
the same DTD as Spring’s XML bean factories. The default configuration file is
/WEB-INF/views.xml . | ResourceBundleViewResolver
| Implementation of ViewResolver that uses bean definitions in a ResourceBundle ,
specified by the bundle base name. Typically you define the bundle in a properties
file, located in the classpath. The default file name is views.properties . | UrlBasedViewResolver
| Simple implementation of the ViewResolver interface that effects the direct
resolution of logical view names to URLs, without an explicit mapping definition. This
is appropriate if your logical names match the names of your view resources in a
straightforward manner, without the need for arbitrary mappings. | InternalResourceViewResolver
| Convenient subclass of UrlBasedViewResolver that supports InternalResourceView (in
effect, Servlets and JSPs) and subclasses such as JstlView and TilesView . You can
specify the view class for all views generated by this resolver by using
setViewClass(..) . See the UrlBasedViewResolver javadocs for details. | VelocityViewResolver / FreeMarkerViewResolver
| Convenient subclass of UrlBasedViewResolver that supports VelocityView (in effect,
Velocity templates) or FreeMarkerView ,respectively, and custom subclasses of them. | ContentNegotiatingViewResolver
| Implementation of the ViewResolver interface that resolves a view based on the
request file name or Accept header. See Section 16.5.4, “ContentNegotiatingViewResolver”. |
As an example, with JSP as a view technology, you can use the UrlBasedViewResolver .
This view resolver translates a view name to a URL and hands the request over to the
RequestDispatcher to render the view.
<bean id="viewResolver"
class="org.springframework.web.servlet.view.UrlBasedViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
When returning test as a logical view name, this view resolver forwards the request to
the RequestDispatcher that will send the request to /WEB-INF/jsp/test.jsp .
When you combine different view technologies in a web application, you can use the
ResourceBundleViewResolver :
<bean id="viewResolver"
class="org.springframework.web.servlet.view.ResourceBundleViewResolver">
<property name="basename" value="views"/>
<property name="defaultParentView" value="parentView"/>
</bean>
The ResourceBundleViewResolver inspects the ResourceBundle identified by the
basename, and for each view it is supposed to resolve, it uses the value of the property
[viewname].(class) as the view class and the value of the property [viewname].url as
the view url. Examples can be found in the next chapter which covers view technologies.
As you can see, you can identify a parent view, from which all views in the properties
file "extend". This way you can specify a default view class, for example.
![[Note]](images/note.png) | Note |
---|
Subclasses of AbstractCachingViewResolver cache view instances that they resolve.
Caching improves performance of certain view technologies. It’s possible to turn off the
cache by setting the cache property to false . Furthermore, if you must refresh a
certain view at runtime (for example when a Velocity template is modified), you can use
the removeFromCache(String viewName, Locale loc) method.
|
16.5.2 Chaining ViewResolvers
Spring supports multiple view resolvers. Thus you can chain resolvers and, for example,
override specific views in certain circumstances. You chain view resolvers by adding
more than one resolver to your application context and, if necessary, by setting the
order property to specify ordering. Remember, the higher the order property, the later
the view resolver is positioned in the chain.
In the following example, the chain of view resolvers consists of two resolvers, an
InternalResourceViewResolver , which is always automatically positioned as the last
resolver in the chain, and an XmlViewResolver for specifying Excel views. Excel views
are not supported by the InternalResourceViewResolver .
<bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
<bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver">
<property name="order" value="1"/>
<property name="location" value="/WEB-INF/views.xml"/>
</bean>
<beans>
<bean name="report" class="org.springframework.example.ReportExcelView"/>
</beans>
If a specific view resolver does not result in a view, Spring examines the context for
other view resolvers. If additional view resolvers exist, Spring continues to inspect
them until a view is resolved. If no view resolver returns a view, Spring throws a
ServletException .
The contract of a view resolver specifies that a view resolver can return null to
indicate the view could not be found. Not all view resolvers do this, however, because
in some cases, the resolver simply cannot detect whether or not the view exists. For
example, the InternalResourceViewResolver uses the RequestDispatcher internally, and
dispatching is the only way to figure out if a JSP exists, but this action can only
execute once. The same holds for the VelocityViewResolver and some others. Check the
javadocs of the specific view resolver to see whether it reports non-existing views.
Thus, putting an InternalResourceViewResolver in the chain in a place other than
the last results in the chain not being fully inspected, because the
InternalResourceViewResolver will always return a view!
16.5.3 Redirecting to views
As mentioned previously, a controller typically returns a logical view name, which a
view resolver resolves to a particular view technology. For view technologies such as
JSPs that are processed through the Servlet or JSP engine, this resolution is usually
handled through the combination of InternalResourceViewResolver and
InternalResourceView , which issues an internal forward or include via the Servlet
API’s RequestDispatcher.forward(..) method or RequestDispatcher.include() method.
For other view technologies, such as Velocity, XSLT, and so on, the view itself writes
the content directly to the response stream.
It is sometimes desirable to issue an HTTP redirect back to the client, before the view
is rendered. This is desirable, for example, when one controller has been called with
POST data, and the response is actually a delegation to another controller (for
example on a successful form submission). In this case, a normal internal forward will
mean that the other controller will also see the same POST data, which is potentially
problematic if it can confuse it with other expected data. Another reason to perform a
redirect before displaying the result is to eliminate the possibility of the user
submitting the form data multiple times. In this scenario, the browser will first send
an initial POST ; it will then receive a response to redirect to a different URL; and
finally the browser will perform a subsequent GET for the URL named in the redirect
response. Thus, from the perspective of the browser, the current page does not reflect
the result of a POST but rather of a GET . The end effect is that there is no way the
user can accidentally re- POST the same data by performing a refresh. The refresh
forces a GET of the result page, not a resend of the initial POST data.
One way to force a redirect as the result of a controller response is for the controller
to create and return an instance of Spring’s RedirectView . In this case,
DispatcherServlet does not use the normal view resolution mechanism. Rather because it
has been given the (redirect) view already, the DispatcherServlet simply instructs the
view to do its work.
The RedirectView issues an HttpServletResponse.sendRedirect() call that returns to
the client browser as an HTTP redirect. By default all model attributes are considered
to be exposed as URI template variables in the redirect URL. Of the remaining attributes
those that are primitive types or collections/arrays of primitive types are
automatically appended as query parameters.
Appending primitive type attributes as query parameters may be the desired result if a
model instance was prepared specifically for the redirect. However, in annotated
controllers the model may contain additional attributes added for rendering purposes
(e.g. drop-down field values). To avoid the possibility of having such attributes appear
in the URL an annotated controller can declare an argument of type RedirectAttributes
and use it to specify the exact attributes to make available to RedirectView . If the
controller method decides to redirect, the content of RedirectAttributes is used.
Otherwise the content of the model is used.
Note that URI template variables from the present request are automatically made
available when expanding a redirect URL and do not need to be added explicitly neither
through Model nor RedirectAttributes . For example:
@RequestMapping(value = "/files/{path}", method = RequestMethod.POST)
public String upload(...) {
return "redirect:files/{path}";
}
If you use RedirectView and the view is created by the controller itself, it is
recommended that you configure the redirect URL to be injected into the controller so
that it is not baked into the controller but configured in the context along with the
view names. The next section discusses this process.
While the use of RedirectView works fine, if the controller itself creates the
RedirectView , there is no avoiding the fact that the controller is aware that a
redirection is happening. This is really suboptimal and couples things too tightly. The
controller should not really care about how the response gets handled. In general it
should operate only in terms of view names that have been injected into it.
The special redirect: prefix allows you to accomplish this. If a view name is returned
that has the prefix redirect: , the UrlBasedViewResolver (and all subclasses) will
recognize this as a special indication that a redirect is needed. The rest of the view
name will be treated as the redirect URL.
The net effect is the same as if the controller had returned a RedirectView , but now
the controller itself can simply operate in terms of logical view names. A logical view
name such as redirect:/myapp/some/resource will redirect relative to the current
Servlet context, while a name such as redirect:http://myhost.com/some/arbitrary/path
will redirect to an absolute URL.
It is also possible to use a special forward: prefix for view names that are
ultimately resolved by UrlBasedViewResolver and subclasses. This creates an
InternalResourceView (which ultimately does a RequestDispatcher.forward() ) around
the rest of the view name, which is considered a URL. Therefore, this prefix is not
useful with InternalResourceViewResolver and InternalResourceView (for JSPs for
example). But the prefix can be helpful when you are primarily using another view
technology, but still want to force a forward of a resource to be handled by the
Servlet/JSP engine. (Note that you may also chain multiple view resolvers, instead.)
As with the redirect: prefix, if the view name with the forward: prefix is injected
into the controller, the controller does not detect that anything special is happening
in terms of handling the response.
16.5.4 ContentNegotiatingViewResolver
The ContentNegotiatingViewResolver does not resolve views itself but rather delegates
to other view resolvers, selecting the view that resembles the representation requested
by the client. Two strategies exist for a client to request a representation from the
server:
-
Use a distinct URI for each resource, typically by using a different file extension in
the URI. For example, the URI
http://www.example.com/users/fred.pdf requests a PDF
representation of the user fred, and http://www.example.com/users/fred.xml requests
an XML representation.
-
Use the same URI for the client to locate the resource, but set the
Accept HTTP
request header to list the media
types that it understands. For example, an HTTP request for
http://www.example.com/users/fred with an Accept header set to application/pdf
requests a PDF representation of the user fred, while
http://www.example.com/users/fred with an Accept header set to text/xml requests
an XML representation. This strategy is known as
content negotiation.
![[Note]](images/note.png) | Note |
---|
One issue with the Accept header is that it is impossible to set it in a web browser
within HTML. For example, in Firefox, it is fixed to:
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
For this reason it is common to see the use of a distinct URI for each representation
when developing browser based web applications.
|
To support multiple representations of a resource, Spring provides the
ContentNegotiatingViewResolver to resolve a view based on the file extension or
Accept header of the HTTP request. ContentNegotiatingViewResolver does not perform
the view resolution itself but instead delegates to a list of view resolvers that you
specify through the bean property ViewResolvers .
The ContentNegotiatingViewResolver selects an appropriate View to handle the request
by comparing the request media type(s) with the media type (also known as
Content-Type ) supported by the View associated with each of its ViewResolvers . The
first View in the list that has a compatible Content-Type returns the representation
to the client. If a compatible view cannot be supplied by the ViewResolver chain, then
the list of views specified through the DefaultViews property will be consulted. This
latter option is appropriate for singleton Views that can render an appropriate
representation of the current resource regardless of the logical view name. The Accept
header may include wild cards, for example text/* , in which case a View whose
Content-Type was text/xml is a compatible match.
To support the resolution of a view based on a file extension, use the
ContentNegotiatingViewResolver bean property mediaTypes to specify a mapping of file
extensions to media types. For more information on the algorithm used to determine the
request media type, refer to the API documentation for ContentNegotiatingViewResolver .
Here is an example configuration of a ContentNegotiatingViewResolver:
<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
<property name="mediaTypes">
<map>
<entry key="atom" value="application/atom+xml"/>
<entry key="html" value="text/html"/>
<entry key="json" value="application/json"/>
</map>
</property>
<property name="viewResolvers">
<list>
<bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/>
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
</list>
</property>
<property name="defaultViews">
<list>
<bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView" />
</list>
</property>
</bean>
<bean id="content" class="com.springsource.samples.rest.SampleContentAtomView"/>
The InternalResourceViewResolver handles the translation of view names and JSP pages,
while the BeanNameViewResolver returns a view based on the name of a bean. (See
"Resolving views with the ViewResolver interface" for more
details on how Spring looks up and instantiates a view.) In this example, the content
bean is a class that inherits from AbstractAtomFeedView , which returns an Atom RSS
feed. For more information on creating an Atom Feed representation, see the section Atom
Views.
In the above configuration, if a request is made with an .php extension, the view
resolver looks for a view that matches the text/html media type. The
InternalResourceViewResolver provides the matching view for text/html . If the
request is made with the file extension .atom , the view resolver looks for a view that
matches the application/atom+xml media type. This view is provided by the
BeanNameViewResolver that maps to the SampleContentAtomView if the view name
returned is content . If the request is made with the file extension .json , the
MappingJackson2JsonView instance from the DefaultViews list will be selected
regardless of the view name. Alternatively, client requests can be made without a file
extension but with the Accept header set to the preferred media-type, and the same
resolution of request to views would occur.
![[Note]](images/note.png) | Note |
---|
If ContentNegotiatingViewResolver 's list of ViewResolvers is not configured
explicitly, it automatically uses any ViewResolvers defined in the application context.
|
The corresponding controller code that returns an Atom RSS feed for a URI of the form
http://localhost/content.atom or http://localhost/content with an Accept header of
application/atom+xml is shown below.
@Controller
public class ContentController {
private List<SampleContent> contentList = new ArrayList<SampleContent>();
@RequestMapping(value="/content", method=RequestMethod.GET)
public ModelAndView getContent() {
ModelAndView mav = new ModelAndView();
mav.setViewName("content");
mav.addObject("sampleContentList", contentList);
return mav;
}
}
16.6 Using flash attributes
Flash attributes provide a way for one request to store attributes intended for use in
another. This is most commonly needed when redirecting — for example, the
Post/Redirect/Get pattern. Flash attributes are saved temporarily before the
redirect (typically in the session) to be made available to the request after the
redirect and removed immediately.
Spring MVC has two main abstractions in support of flash attributes. FlashMap is used
to hold flash attributes while FlashMapManager is used to store, retrieve, and manage
FlashMap instances.
Flash attribute support is always "on" and does not need to enabled explicitly although
if not used, it never causes HTTP session creation. On each request there is an "input"
FlashMap with attributes passed from a previous request (if any) and an "output"
FlashMap with attributes to save for a subsequent request. Both FlashMap instances
are accessible from anywhere in Spring MVC through static methods in
RequestContextUtils .
Annotated controllers typically do not need to work with FlashMap directly. Instead an
@RequestMapping method can accept an argument of type RedirectAttributes and use it
to add flash attributes for a redirect scenario. Flash attributes added via
RedirectAttributes are automatically propagated to the "output" FlashMap. Similarly
after the redirect attributes from the "input" FlashMap are automatically added to the
Model of the controller serving the target URL.
Spring MVC provides a mechanism for building and encoding a URI using
UriComponentsBuilder and UriComponents .
For example you can expand and encode a URI template string:
UriComponents uriComponents = UriComponentsBuilder.fromUriString(
"http://example.com/hotels/{hotel}/bookings/{booking}").build();
URI uri = uriComponents.expand("42", "21").encode().toUri();
Note that UriComponents is immutable and the expand() and encode() operations
return new instances if necessary.
You can also expand and encode using individual URI components:
UriComponents uriComponents = UriComponentsBuilder.newInstance()
.scheme("http").host("example.com").path("/hotels/{hotel}/bookings/{booking}").build()
.expand("42", "21")
.encode();
In a Servlet environment the ServletUriComponentsBuilder sub-class provides static
factory methods to copy available URL information from a Servlet requests:
HttpServletRequest request = ...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request)
.replaceQueryParam("accountId", "{id}").build()
.expand("123")
.encode();
Alternatively, you may choose to copy a subset of the available information up to and
including the context path:
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request)
.path("/accounts").build()
Or in cases where the DispatcherServlet is mapped by name (e.g. /main/* ), you can
also have the literal part of the servlet mapping included:
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request)
.path("/accounts").build()
16.8 Building URIs to Controllers and methods
Spring MVC provides another mechanism for building and encoding URIs that link to
Controllers and methods defined within an application.
MvcUriComponentsBuilder
extends UriComponentsBuilder and provides such possibilities.
Given this Controller:
@Controller
@RequestMapping("/hotels/{hotel}")
public class BookingController {
@RequestMapping("/bookings/{booking}")
public String getBooking(@PathVariable Long booking) {
}
and using the MvcUriComponentsBuilder , the previous example is now:
UriComponents uriComponents = MvcUriComponentsBuilder
.fromMethodName(BookingController.class, "getBooking",21).buildAndExpand(42);
URI uri = uriComponents.encode().toUri();
The MvcUriComponentsBuilder can also create "mock Controllers", thus enabling to create
URIs by coding against the actual Controller’s API:
UriComponents uriComponents = MvcUriComponentsBuilder
.fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);
URI uri = uriComponents.encode().toUri();
Most parts of Spring’s architecture support internationalization, just as the Spring web
MVC framework does. DispatcherServlet enables you to automatically resolve messages
using the client’s locale. This is done with LocaleResolver objects.
When a request comes in, the DispatcherServlet looks for a locale resolver, and if it
finds one it tries to use it to set the locale. Using the RequestContext.getLocale()
method, you can always retrieve the locale that was resolved by the locale resolver.
In addition to automatic locale resolution, you can also attach an interceptor to the
handler mapping (see Section 16.4.1, “Intercepting requests with a HandlerInterceptor” for more information on handler
mapping interceptors) to change the locale under specific circumstances, for example,
based on a parameter in the request.
Locale resolvers and interceptors are defined in the
org.springframework.web.servlet.i18n package and are configured in your application
context in the normal way. Here is a selection of the locale resolvers included in
Spring.
16.9.1 Obtaining Time Zone Information
In addition to obtaining the client’s locale, it is often useful to know their time zone.
The LocaleContextResolver interface offers an extension to LocaleResolver that allows
resolvers to provide a richer LocaleContext , which may include time zone information.
When available, the user’s TimeZone can be obtained using the
RequestContext.getTimeZone() method. Time zone information will automatically be used
by Date/Time Converter and Formatter objects registered with Spring’s
ConversionService .
16.9.2 AcceptHeaderLocaleResolver
This locale resolver inspects the accept-language header in the request that was sent
by the client (e.g., a web browser). Usually this header field contains the locale of
the client’s operating system. Note that this resolver does not support time zone
information.
16.9.3 CookieLocaleResolver
This locale resolver inspects a Cookie that might exist on the client to see if a
Locale or TimeZone is specified. If so, it uses the specified details. Using the
properties of this locale resolver, you can specify the name of the cookie as well as the
maximum age. Find below an example of defining a CookieLocaleResolver .
<bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver">
<property name="cookieName" value="clientlanguage"/>
<property name="cookieMaxAge" value="100000">
</bean>
Table 16.4. CookieLocaleResolver properties
Property | Default | Description |
---|
cookieName | classname + LOCALE | The name of the cookie | cookieMaxAge | Integer.MAX_INT | The maximum time a cookie will stay persistent on the client. If -1 is specified, the
cookie will not be persisted; it will only be available until the client shuts down
their browser. | cookiePath | / | Limits the visibility of the cookie to a certain part of your site. When cookiePath is
specified, the cookie will only be visible to that path and the paths below it. |
16.9.4 SessionLocaleResolver
The SessionLocaleResolver allows you to retrieve Locale and TimeZone from the
session that might be associated with the user’s request.
16.9.5 LocaleChangeInterceptor
You can enable changing of locales by adding the LocaleChangeInterceptor to one of the
handler mappings (see Section 16.4, “Handler mappings”). It will detect a parameter in the request
and change the locale. It calls setLocale() on the LocaleResolver that also exists
in the context. The following example shows that calls to all *.view resources
containing a parameter named siteLanguage will now change the locale. So, for example,
a request for the following URL, http://www.sf.net/home.view?siteLanguage=nl will
change the site language to Dutch.
<bean id="localeChangeInterceptor"
class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor">
<property name="paramName" value="siteLanguage"/>
</bean>
<bean id="localeResolver"
class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/>
<bean id="urlMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="interceptors">
<list>
<ref bean="localeChangeInterceptor"/>
</list>
</property>
<property name="mappings">
<value>/*/.view=someController</value>
</property>
</bean>
16.10.1 Overview of themes
You can apply Spring Web MVC framework themes to set the overall look-and-feel of your
application, thereby enhancing user experience. A theme is a collection of static
resources, typically style sheets and images, that affect the visual style of the
application.
To use themes in your web application, you must set up an implementation of the
org.springframework.ui.context.ThemeSource interface. The WebApplicationContext
interface extends ThemeSource but delegates its responsibilities to a dedicated
implementation. By default the delegate will be an
org.springframework.ui.context.support.ResourceBundleThemeSource implementation that
loads properties files from the root of the classpath. To use a custom ThemeSource
implementation or to configure the base name prefix of the ResourceBundleThemeSource ,
you can register a bean in the application context with the reserved name themeSource .
The web application context automatically detects a bean with that name and uses it.
When using the ResourceBundleThemeSource , a theme is defined in a simple properties
file. The properties file lists the resources that make up the theme. Here is an example:
styleSheet=/themes/cool/style.css
background=/themes/cool/img/coolBg.jpg
The keys of the properties are the names that refer to the themed elements from view
code. For a JSP, you typically do this using the spring:theme custom tag, which is
very similar to the spring:message tag. The following JSP fragment uses the theme
defined in the previous example to customize the look and feel:
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
<html>
<head>
<link rel="stylesheet" href="<spring:theme code=styleSheet/>" type="text/css"/>
</head>
<body style="background=<spring:theme code=background/>">
...
</body>
</html>
By default, the ResourceBundleThemeSource uses an empty base name prefix. As a result,
the properties files are loaded from the root of the classpath. Thus you would put the
cool.properties theme definition in a directory at the root of the classpath, for
example, in /WEB-INF/classes . The ResourceBundleThemeSource uses the standard Java
resource bundle loading mechanism, allowing for full internationalization of themes. For
example, we could have a /WEB-INF/classes/cool_nl.properties that references a special
background image with Dutch text on it.
After you define themes, as in the preceding section, you decide which theme to use. The
DispatcherServlet will look for a bean named themeResolver to find out which
ThemeResolver implementation to use. A theme resolver works in much the same way as a
LocaleResolver . It detects the theme to use for a particular request and can also
alter the request’s theme. The following theme resolvers are provided by Spring:
Table 16.5. ThemeResolver implementations
Class | Description |
---|
FixedThemeResolver
| Selects a fixed theme, set using the defaultThemeName property. | SessionThemeResolver
| The theme is maintained in the user’s HTTP session. It only needs to be set once for
each session, but is not persisted between sessions. | CookieThemeResolver
| The selected theme is stored in a cookie on the client. |
Spring also provides a ThemeChangeInterceptor that allows theme changes on every
request with a simple request parameter.
16.11 Spring’s multipart (file upload) support
Spring’s built-in multipart support handles file uploads in web applications. You enable
this multipart support with pluggable MultipartResolver objects, defined in the
org.springframework.web.multipart package. Spring provides one MultipartResolver
implementation for use with Commons
FileUpload and another for use with Servlet 3.0 multipart request parsing.
By default, Spring does no multipart handling, because some developers want to handle
multiparts themselves. You enable Spring multipart handling by adding a multipart
resolver to the web application’s context. Each request is inspected to see if it
contains a multipart. If no multipart is found, the request continues as expected. If a
multipart is found in the request, the MultipartResolver that has been declared in
your context is used. After that, the multipart attribute in your request is treated
like any other attribute.
16.11.2 Using a MultipartResolver with Commons FileUpload
The following example shows how to use the CommonsMultipartResolver :
<bean id="multipartResolver"
class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<property name="maxUploadSize" value="100000"/>
</bean>
Of course you also need to put the appropriate jars in your classpath for the multipart
resolver to work. In the case of the CommonsMultipartResolver , you need to use
commons-fileupload.jar .
When the Spring DispatcherServlet detects a multi-part request, it activates the
resolver that has been declared in your context and hands over the request. The resolver
then wraps the current HttpServletRequest into a MultipartHttpServletRequest that
supports multipart file uploads. Using the MultipartHttpServletRequest , you can get
information about the multiparts contained by this request and actually get access to
the multipart files themselves in your controllers.
16.11.3 Using a MultipartResolver with Servlet 3.0
In order to use Servlet 3.0 based multipart parsing, you need to mark the
DispatcherServlet with a "multipart-config" section in web.xml , or with a
javax.servlet.MultipartConfigElement in programmatic Servlet registration, or in case
of a custom Servlet class possibly with a javax.servlet.annotation.MultipartConfig
annotation on your Servlet class. Configuration settings such as maximum sizes or
storage locations need to be applied at that Servlet registration level as Servlet 3.0
does not allow for those settings to be done from the MultipartResolver.
Once Servlet 3.0 multipart parsing has been enabled in one of the above mentioned ways
you can add the StandardServletMultipartResolver to your Spring configuration:
<bean id="multipartResolver"
class="org.springframework.web.multipart.support.StandardServletMultipartResolver">
</bean>
16.11.4 Handling a file upload in a form
After the MultipartResolver completes its job, the request is processed like any
other. First, create a form with a file input that will allow the user to upload a form.
The encoding attribute ( enctype="multipart/form-data" ) lets the browser know how to
encode the form as multipart request:
<html>
<head>
<title>Upload a file please</title>
</head>
<body>
<h1>Please upload a file</h1>
<form method="post" action="/form" enctype="multipart/form-data">
<input type="text" name="name"/>
<input type="file" name="file"/>
<input type="submit"/>
</form>
</body>
</html>
The next step is to create a controller that handles the file upload. This controller is
very similar to a normal annotated @Controller , except that we
use MultipartHttpServletRequest or MultipartFile in the method parameters:
@Controller
public class FileUploadController {
@RequestMapping(value = "/form", method = RequestMethod.POST)
public String handleFormUpload(@RequestParam("name") String name,
@RequestParam("file") MultipartFile file) {
if (!file.isEmpty()) {
byte[] bytes = file.getBytes();
return "redirect:uploadSuccess";
}
return "redirect:uploadFailure";
}
}
Note how the @RequestParam method parameters map to the input elements declared in the
form. In this example, nothing is done with the byte[] , but in practice you can save
it in a database, store it on the file system, and so on.
When using Servlet 3.0 multipart parsing you can also use javax.servlet.http.Part for
the method parameter:
@Controller
public class FileUploadController {
@RequestMapping(value = "/form", method = RequestMethod.POST)
public String handleFormUpload(@RequestParam("name") String name,
@RequestParam("file") Part file) {
InputStream inputStream = file.getInputStream();
return "redirect:uploadSuccess";
}
}
16.11.5 Handling a file upload request from programmatic clients
Multipart requests can also be submitted from non-browser clients in a RESTful service
scenario. All of the above examples and configuration apply here as well. However,
unlike browsers that typically submit files and simple form fields, a programmatic
client can also send more complex data of a specific content type — for example a
multipart request with a file and second part with JSON formatted data:
POST /someUrl
Content-Type: multipart/mixed
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="meta-data"
Content-Type: application/json; charset=UTF-8
Content-Transfer-Encoding: 8bit
{
"name": "value"
}
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="file-data"; filename="file.properties"
Content-Type: text/xml
Content-Transfer-Encoding: 8bit
... File Data ...
You could access the part named "meta-data" with a @RequestParam("meta-data") String
metadata controller method argument. However, you would probably prefer to accept a
strongly typed object initialized from the JSON formatted data in the body of the
request part, very similar to the way @RequestBody converts the body of a
non-multipart request to a target object with the help of an HttpMessageConverter .
You can use the @RequestPart annotation instead of the @RequestParam annotation for
this purpose. It allows you to have the content of a specific multipart passed through
an HttpMessageConverter taking into consideration the 'Content-Type' header of the
multipart:
@RequestMapping(value="/someUrl", method = RequestMethod.POST)
public String onSubmit(@RequestPart("meta-data") MetaData metadata,
@RequestPart("file-data") MultipartFile file) {
}
Notice how MultipartFile method arguments can be accessed with @RequestParam or with
@RequestPart interchangeably. However, the @RequestPart("meta-data") MetaData method
argument in this case is read as JSON content based on its 'Content-Type' header and
converted with the help of the MappingJackson2HttpMessageConverter .
16.12 Handling exceptions
16.12.1 HandlerExceptionResolver
Spring HandlerExceptionResolver implementations deal with unexpected exceptions that
occur during controller execution. A HandlerExceptionResolver somewhat resembles the
exception mappings you can define in the web application descriptor web.xml . However,
they provide a more flexible way to do so. For example they provide information about
which handler was executing when the exception was thrown. Furthermore, a programmatic
way of handling exceptions gives you more options for responding appropriately before
the request is forwarded to another URL (the same end result as when you use the Servlet
specific exception mappings).
Besides implementing the HandlerExceptionResolver interface, which is only a matter of
implementing the resolveException(Exception, Handler) method and returning a
ModelAndView , you may also use the provided SimpleMappingExceptionResolver or create
@ExceptionHandler methods. The SimpleMappingExceptionResolver enables you to take
the class name of any exception that might be thrown and map it to a view name. This is
functionally equivalent to the exception mapping feature from the Servlet API, but it is
also possible to implement more finely grained mappings of exceptions from different
handlers. The @ExceptionHandler annotation on the other hand can be used on methods
that should be invoked to handle an exception. Such methods may be defined locally
within an @Controller or may apply to many @Controller classes when defined within an
@ControllerAdvice class. The following sections explain this in more detail.
16.12.2 @ExceptionHandler
The HandlerExceptionResolver interface and the SimpleMappingExceptionResolver
implementations allow you to map Exceptions to specific views declaratively along with
some optional Java logic before forwarding to those views. However, in some cases,
especially when relying on @ResponseBody methods rather than on view resolution, it
may be more convenient to directly set the status of the response and optionally write
error content to the body of the response.
You can do that with @ExceptionHandler methods. When declared within a controller such
methods apply to exceptions raised by @RequestMapping methods of that contoroller (or
any of its sub-classes). You can also declare an @ExceptionHandler method within an
@ControllerAdvice class in which case it handles exceptions from @RequestMapping
methods from many controllers. Below is an example of a controller-local
@ExceptionHandler method:
@Controller
public class SimpleController {
@ExceptionHandler(IOException.class)
public ResponseEntity<String> handleIOException(IOException ex) {
return responseEntity;
}
}
The @ExceptionHandler value can be set to an array of Exception types. If an exception
is thrown that matches one of the types in the list, then the method annotated with the
matching @ExceptionHandler will be invoked. If the annotation value is not set then
the exception types listed as method arguments are used.
Much like standard controller methods annotated with a @RequestMapping annotation, the
method arguments and return values of @ExceptionHandler methods can be flexible. For
example, the HttpServletRequest can be accessed in Servlet environments and the
PortletRequest in Portlet environments. The return type can be a String , which is
interpreted as a view name, a ModelAndView object, a ResponseEntity , or you can also
add the @ResponseBody to have the method return value converted with message
converters and written to the response stream.
16.12.3 Handling Standard Spring MVC Exceptions
Spring MVC may raise a number of exceptions while processing a request. The
SimpleMappingExceptionResolver can easily map any exception to a default error view as
needed. However, when working with clients that interpret responses in an automated way
you will want to set specific status code on the response. Depending on the exception
raised the status code may indicate a client error (4xx) or a server error (5xx).
The DefaultHandlerExceptionResolver translates Spring MVC exceptions to specific error
status codes. It is registered by default with the MVC namespace, the MVC Java config,
and also by the the DispatcherServlet (i.e. when not using the MVC namespace or Java
config). Listed below are some of the exceptions handled by this resolver and the
corresponding status codes:
The DefaultHandlerExceptionResolver works transparently by setting the status of the
response. However, it stops short of writing any error content to the body of the
response while your application may need to add developer-friendly content to every
error response for example when providing a REST API. You can prepare a ModelAndView
and render error content through view resolution — i.e. by configuring a
ContentNegotiatingViewResolver , MappingJacksonJsonView , and so on. However, you may
prefer to use @ExceptionHandler methods instead.
If you prefer to write error content via @ExceptionHandler methods you can extend
ResponseEntityExceptionHandler instead. This is a convenient base for
@ControllerAdvice classes providing an @ExceptionHandler method to handle standard
Spring MVC exceptions and return ResponseEntity . That allows you to customize the
response and write error content with message converters. See the
ResponseEntityExceptionHandler javadocs for more details.
16.12.4 Annotating Business Exceptions With @ResponseStatus
A business exception can be annotated with @ResponseStatus . When the exception is
raised, the ResponseStatusExceptionResolver handles it by setting the status of the
response accordingly. By default the DispatcherServlet registers the
ResponseStatusExceptionResolver and it is available for use.
16.12.5 Customizing the Default Servlet Container Error Page
When the status of the response is set to an error status code and the body of the
response is empty, Servlet containers commonly render an HTML formatted error page. To
customize the default error page of the container, you can declare an <error-page>
element in web.xml . Up until Servlet 3, that element had to be mapped to a specific
status code or exception type. Starting with Servlet 3 an error page does not need to be
mapped, which effectively means the specified location customizes the default Servlet
container error page.
<error-page>
<location>/error</location>
</error-page>
Note that the actual location for the error page can be a JSP page or some other URL
within the container including one handled through an @Controller method:
When writing error information, the status code and the error message set on the
HttpServletResponse can be accessed through request attributes in a controller:
@Controller
public class ErrorController {
@RequestMapping(value="/error", produces="application/json")
@ResponseBody
public Map<String, Object> handle(HttpServletRequest request) {
Map<String, Object> map = new HashMap<String, Object>();
map.put("status", request.getAttribute("javax.servlet.error.status_code"));
map.put("reason", request.getAttribute("javax.servlet.error.message"));
return map;
}
}
or in a JSP:
<%@ page contentType="application/json" pageEncoding="UTF-8"%>
{
status:<%=request.getAttribute("javax.servlet.error.status_code") %>,
reason:<%=request.getAttribute("javax.servlet.error.message") %>
}
16.13 Convention over configuration support
For a lot of projects, sticking to established conventions and having reasonable
defaults is just what they (the projects) need, and Spring Web MVC now has explicit
support for convention over configuration. What this means is that if you establish
a set of naming conventions and suchlike, you can substantially cut down on the
amount of configuration that is required to set up handler mappings, view resolvers,
ModelAndView instances, etc. This is a great boon with regards to rapid prototyping,
and can also lend a degree of (always good-to-have) consistency across a codebase should
you choose to move forward with it into production.
Convention-over-configuration support addresses the three core areas of MVC: models,
views, and controllers.
16.13.1 The Controller ControllerClassNameHandlerMapping
The ControllerClassNameHandlerMapping class is a HandlerMapping implementation that
uses a convention to determine the mapping between request URLs and the Controller
instances that are to handle those requests.
Consider the following simple Controller implementation. Take special notice of the
name of the class.
public class ViewShoppingCartController implements Controller {
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
}
}
Here is a snippet from the corresponding Spring Web MVC configuration file:
<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/>
<bean id="viewShoppingCart" class="x.y.z.ViewShoppingCartController">
</bean>
The ControllerClassNameHandlerMapping finds all of the various handler (or
Controller ) beans defined in its application context and strips Controller off the
name to define its handler mappings. Thus, ViewShoppingCartController maps to the
/viewshoppingcart* request URL.
Let’s look at some more examples so that the central idea becomes immediately familiar.
(Notice all lowercase in the URLs, in contrast to camel-cased Controller class names.)
-
WelcomeController maps to the /welcome* request URL
-
HomeController maps to the /home* request URL
-
IndexController maps to the /index* request URL
-
RegisterController maps to the /register* request URL
In the case of MultiActionController handler classes, the mappings generated are
slightly more complex. The Controller names in the following examples are assumed to
be MultiActionController implementations:
-
AdminController maps to the /admin/* request URL
-
CatalogController maps to the /catalog/* request URL
If you follow the convention of naming your Controller implementations as
xxxController , the ControllerClassNameHandlerMapping saves you the tedium of
defining and maintaining a potentially looooong SimpleUrlHandlerMapping (or
suchlike).
The ControllerClassNameHandlerMapping class extends the AbstractHandlerMapping base
class so you can define HandlerInterceptor instances and everything else just as you
would with many other HandlerMapping implementations.
16.13.2 The Model ModelMap (ModelAndView)
The ModelMap class is essentially a glorified Map that can make adding objects that
are to be displayed in (or on) a View adhere to a common naming convention. Consider
the following Controller implementation; notice that objects are added to the
ModelAndView without any associated name specified.
public class DisplayShoppingCartController implements Controller {
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
List cartItems =
User user =
ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name
mav.addObject(cartItems); <-- look ma, no name, just the object
mav.addObject(user); <-- and again ma!
return mav;
}
}
The ModelAndView class uses a ModelMap class that is a custom Map implementation
that automatically generates a key for an object when an object is added to it. The
strategy for determining the name for an added object is, in the case of a scalar object
such as User , to use the short class name of the object’s class. The following
examples are names that are generated for scalar objects put into a ModelMap instance.
-
An
x.y.User instance added will have the name user generated.
-
An
x.y.Registration instance added will have the name registration generated.
-
An
x.y.Foo instance added will have the name foo generated.
-
A
java.util.HashMap instance added will have the name hashMap generated. You
probably want to be explicit about the name in this case because hashMap is less
than intuitive.
-
Adding
null will result in an IllegalArgumentException being thrown. If the object
(or objects) that you are adding could be null , then you will also want to be
explicit about the name.
The strategy for generating a name after adding a Set or a List is to peek into the
collection, take the short class name of the first object in the collection, and use
that with List appended to the name. The same applies to arrays although with arrays
it is not necessary to peek into the array contents. A few examples will make the
semantics of name generation for collections clearer:
-
An
x.y.User[] array with zero or more x.y.User elements added will have the name
userList generated.
-
An
x.y.Foo[] array with zero or more x.y.User elements added will have the name
fooList generated.
-
A
java.util.ArrayList with one or more x.y.User elements added will have the name
userList generated.
-
A
java.util.HashSet with one or more x.y.Foo elements added will have the name
fooList generated.
-
An empty
java.util.ArrayList will not be added at all (in effect, the
addObject(..) call will essentially be a no-op).
16.13.3 The View - RequestToViewNameTranslator
The RequestToViewNameTranslator interface determines a logical View name when no
such logical view name is explicitly supplied. It has just one implementation, the
DefaultRequestToViewNameTranslator class.
The DefaultRequestToViewNameTranslator maps request URLs to logical view names, as
with this example:
public class RegistrationController implements Controller {
public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
ModelAndView mav = new ModelAndView();
return mav;
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="viewNameTranslator"
class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/>
<bean class="x.y.RegistrationController">
</bean>
<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/>
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
</beans>
Notice how in the implementation of the handleRequest(..) method no View or logical
view name is ever set on the ModelAndView that is returned. The
DefaultRequestToViewNameTranslator is tasked with generating a logical view name
from the URL of the request. In the case of the above RegistrationController , which is
used in conjunction with the ControllerClassNameHandlerMapping , a request URL of
http://localhost/registration.php results in a logical view name of registration
being generated by the DefaultRequestToViewNameTranslator . This logical view name is
then resolved into the /WEB-INF/jsp/registration.jsp view by the
InternalResourceViewResolver bean.
![[Tip]](images/tip.png) | Tip |
---|
You do not need to define a DefaultRequestToViewNameTranslator bean explicitly. If you
like the default settings of the DefaultRequestToViewNameTranslator , you can rely on
the Spring Web MVC DispatcherServlet to instantiate an instance of this class if one
is not explicitly configured.
|
Of course, if you need to change the default settings, then you do need to configure
your own DefaultRequestToViewNameTranslator bean explicitly. Consult the comprehensive
DefaultRequestToViewNameTranslator javadocs for details on the various properties
that can be configured.
An ETag (entity tag) is an HTTP response header
returned by an HTTP/1.1 compliant web server used to determine change in content at a
given URL. It can be considered to be the more sophisticated successor to the
Last-Modified header. When a server returns a representation with an ETag header, the
client can use this header in subsequent GETs, in an If-None-Match header. If the
content has not changed, the server returns 304: Not Modified .
Support for ETags is provided by the Servlet filter ShallowEtagHeaderFilter . It is a
plain Servlet Filter, and thus can be used in combination with any web framework. The
ShallowEtagHeaderFilter filter creates so-called shallow ETags (as opposed to deep
ETags, more about that later).The filter caches the content of the rendered JSP (or
other content), generates an MD5 hash over that, and returns that as an ETag header in
the response. The next time a client sends a request for the same resource, it uses that
hash as the If-None-Match value. The filter detects this, renders the view again, and
compares the two hashes. If they are equal, a 304 is returned. This filter will not
save processing power, as the view is still rendered. The only thing it saves is
bandwidth, as the rendered response is not sent back over the wire.
You configure the ShallowEtagHeaderFilter in web.xml :
<filter>
<filter-name>etagFilter</filter-name>
<filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>etagFilter</filter-name>
<servlet-name>petclinic</servlet-name>
</filter-mapping>
16.15 Code-based Servlet container initialization
In a Servlet 3.0+ environment, you have the option of configuring the Servlet container
programmatically as an alternative or in combination with a web.xml file. Below is an
example of registering a DispatcherServlet :
import org.springframework.web.WebApplicationInitializer;
public class MyWebApplicationInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext container) {
XmlWebApplicationContext appContext = new XmlWebApplicationContext();
appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");
ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet(appContext));
registration.setLoadOnStartup(1);
registration.addMapping("/");
}
}
WebApplicationInitializer is an interface provided by Spring MVC that ensures your
implementation is detected and automatically used to initialize any Servlet 3 container.
An abstract base class implementation of WebApplicationInitializer named
AbstractDispatcherServletInitializer makes it even easier to register the
DispatcherServlet by simply overriding methods to specify the servlet mapping and the
location of the DispatcherServlet configuration:
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
@Override
protected Class<?>[] getRootConfigClasses() {
return null;
}
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class[] { MyWebConfig.class };
}
@Override
protected String[] getServletMappings() {
return new String[] { "/" };
}
}
The above example is for an application that uses Java-based Spring configuration. If
using XML-based Spring configuration, extend directly from
AbstractDispatcherServletInitializer :
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {
@Override
protected WebApplicationContext createRootApplicationContext() {
return null;
}
@Override
protected WebApplicationContext createServletApplicationContext() {
XmlWebApplicationContext cxt = new XmlWebApplicationContext();
cxt.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml");
return cxt;
}
@Override
protected String[] getServletMappings() {
return new String[] { "/" };
}
}
AbstractDispatcherServletInitializer also provides a convenient way to add Filter
instances and have them automatically mapped to the DispatcherServlet :
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {
@Override
protected Filter[] getServletFilters() {
return new Filter[] { new HiddenHttpMethodFilter(), new CharacterEncodingFilter() };
}
}
Each filter is added with a default name based on its concrete type and automatically
mapped to the DispatcherServlet .
The isAsyncSupported protected method of AbstractDispatcherServletInitializer
provides a single place to enable async support on the DispatcherServlet and all
filters mapped to it. By default this flag is set to true .
16.16 Configuring Spring MVC
Section 16.2.1, “Special Bean Types In the WebApplicationContext” and Section 16.2.2, “Default DispatcherServlet Configuration” explained about Spring
MVC’s special beans and the default implementations used by the DispatcherServlet . In
this section you’ll learn about two additional ways of configuring Spring MVC. Namely
the MVC Java config and the MVC XML namespace.
The MVC Java config and the MVC namespace provide similar default configuration that
overrides the DispatcherServlet defaults. The goal is to spare most applications from
having to having to create the same configuration and also to provide higher-level
constructs for configuring Spring MVC that serve as a simple starting point and require
little or no prior knowledge of the underlying configuration.
You can choose either the MVC Java config or the MVC namespace depending on your
preference. Also as you will see further below, with the MVC Java config it is easier to
see the underlying configuration as well as to make fine-grained customizations directly
to the created Spring MVC beans. But let’s start from the beginning.
16.16.1 Enabling the MVC Java Config or the MVC XML Namespace
To enable MVC Java config add the annotation @EnableWebMvc to one of your
@Configuration classes:
@Configuration
@EnableWebMvc
public class WebConfig {
}
To achieve the same in XML use the mvc:annotation-driven element in your
DispatcherServlet context (or in your root context if you have no DispatcherServlet
context defined):
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<mvc:annotation-driven />
</beans>
The above registers a RequestMappingHandlerMapping , a RequestMappingHandlerAdapter ,
and an ExceptionHandlerExceptionResolver (among others) in support of processing
requests with annotated controller methods using annotations such as @RequestMapping ,
@ExceptionHandler , and others.
It also enables the following:
-
Spring 3 style type conversion through a ConversionService instance
in addition to the JavaBeans PropertyEditors used for Data Binding.
-
Support for formatting Number fields using the
@NumberFormat annotation
through the ConversionService .
-
Support for formatting Date, Calendar, Long, and Joda Time fields using the
@DateTimeFormat annotation.
-
Support for validating
@Controller inputs with @Valid , if
a JSR-303 Provider is present on the classpath.
-
HttpMessageConverter support for @RequestBody method parameters and @ResponseBody
method return values from @RequestMapping or @ExceptionHandler methods.
This is the complete list of HttpMessageConverters set up by mvc:annotation-driven:
-
ByteArrayHttpMessageConverter converts byte arrays.
-
StringHttpMessageConverter converts strings.
-
ResourceHttpMessageConverter converts to/from
org.springframework.core.io.Resource for all media types.
-
SourceHttpMessageConverter converts to/from a javax.xml.transform.Source .
-
FormHttpMessageConverter converts form data to/from a MultiValueMap<String,
String> .
-
Jaxb2RootElementHttpMessageConverter converts Java objects to/from XML — added if
JAXB2 is present on the classpath.
-
MappingJackson2HttpMessageConverter (or MappingJacksonHttpMessageConverter )
converts to/from JSON — added if Jackson 2 (or Jackson) is present on the classpath.
-
AtomFeedHttpMessageConverter converts Atom feeds — added if Rome is present on the
classpath.
-
RssChannelHttpMessageConverter converts RSS feeds — added if Rome is present on
the classpath.
16.16.2 Customizing the Provided Configuration
To customize the default configuration in Java you simply implement the
WebMvcConfigurer interface or more likely extend the class WebMvcConfigurerAdapter
and override the methods you need. Below is an example of some of the available methods
to override. See
WebMvcConfigurer
for a list of all methods and the javadocs for further details:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
protected void addFormatters(FormatterRegistry registry) {
}
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
}
}
To customize the default configuration of <mvc:annotation-driven /> check what
attributes and sub-elements it supports. You can view the
Spring MVC XML schema or use the code
completion feature of your IDE to discover what attributes and sub-elements are
available. The sample below shows a subset of what is available:
<mvc:annotation-driven conversion-service="conversionService">
<mvc:message-converters>
<bean class="org.example.MyHttpMessageConverter"/>
<bean class="org.example.MyOtherHttpMessageConverter"/>
</mvc:message-converters>
</mvc:annotation-driven>
<bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
<property name="formatters">
<list>
<bean class="org.example.MyFormatter"/>
<bean class="org.example.MyOtherFormatter"/>
</list>
</property>
</bean>
16.16.3 Configuring Interceptors
You can configure HandlerInterceptors or WebRequestInterceptors to be applied to all
incoming requests or restricted to specific URL path patterns.
An example of registering interceptors in Java:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new LocaleInterceptor());
registry.addInterceptor(new ThemeInterceptor()).addPathPatterns("/").excludePathPatterns("/admin/");
registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*");
}
}
And in XML use the <mvc:interceptors> element:
<mvc:interceptors>
<bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor" />
<mvc:interceptor>
<mvc:mapping path="/"/>
<mvc:exclude-mapping path="/admin/"/>
<bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor" />
</mvc:interceptor>
<mvc:interceptor>
<mvc:mapping path="/secure/*"/>
<bean class="org.example.SecurityInterceptor" />
</mvc:interceptor>
</mvc:interceptors>
16.16.4 Configuring Content Negotiation
You can configure how Spring MVC determines the requested media types from the client
for request mapping as well as for content negotiation purposes. The available options
are to check the file extension in the request URI, the "Accept" header, a request
parameter, as well as to fall back on a default content type. By default, file extension
in the request URI is checked first and the "Accept" header is checked next.
For file extensions in the request URI, the MVC Java config and the MVC namespace,
automatically register extensions such as .json , .xml , .rss , and .atom if the
corresponding dependencies such as Jackson, JAXB2, or Rome are present on the classpath.
Additional extensions may be not need to be registered explicitly if they can be
discovered via ServletContext.getMimeType(String) or the Java Activation Framework
(see javax.activation.MimetypesFileTypeMap ). You can register more extensions with the
setUseRegisteredSuffixPatternMatch
method.
The introduction of ContentNegotiationManager also enables selective suffix pattern
matching for incoming requests. For more details, see its javadocs.
Below is an example of customizing content negotiation options through the MVC Java
config:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
configurer.favorPathExtension(false).favorParameter(true);
}
}
In the MVC namespace, the <mvc:annotation-driven> element has a
content-negotiation-manager attribute, which expects a ContentNegotiationManager
that in turn can be created with a ContentNegotiationManagerFactoryBean :
<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" />
<bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
<property name="favorPathExtension" value="false" />
<property name="favorParameter" value="true" />
<property name="mediaTypes" >
<value>
json=application/json
xml=application/xml
</value>
</property>
</bean>
If not using the MVC Java config or the MVC namespace, you’ll need to create an instance
of ContentNegotiationManager and use it to configure RequestMappingHandlerMapping
for request mapping purposes, and RequestMappingHandlerAdapter and
ExceptionHandlerExceptionResolver for content negotiation purposes.
Note that ContentNegotiatingViewResolver now can also be configured with a
ContentNegotiatingViewResolver , so you can use one instance throughout Spring MVC.
In more advanced cases, it may be useful to configure multiple
ContentNegotiationManager instances that in turn may contain custom
ContentNegotiationStrategy implementations. For example you could configure
ExceptionHandlerExceptionResolver with a ContentNegotiationManager that always
resolves the requested media type to "application/json" . Or you may want to plug a
custom strategy that has some logic to select a default content type (e.g. either XML or
JSON) if no content types were requested.
16.16.5 Configuring View Controllers
This is a shortcut for defining a ParameterizableViewController that immediately
forwards to a view when invoked. Use it in static cases when there is no Java controller
logic to execute before the view generates the response.
An example of forwarding a request for "/" to a view called "home" in Java:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addViewControllers(ViewControllerRegistry registry) {
registry.addViewController("/").setViewName("home");
}
}
And the same in XML use the <mvc:view-controller> element:
<mvc:view-controller path="/" view-name="home"/>
16.16.6 Configuring Serving of Resources
This option allows static resource requests following a particular URL pattern to be
served by a ResourceHttpRequestHandler from any of a list of Resource locations.
This provides a convenient way to serve static resources from locations other than the
web application root, including locations on the classpath. The cache-period property
may be used to set far future expiration headers (1 year is the recommendation of
optimization tools such as Page Speed and YSlow) so that they will be more efficiently
utilized by the client. The handler also properly evaluates the Last-Modified header
(if present) so that a 304 status code will be returned as appropriate, avoiding
unnecessary overhead for resources that are already cached by the client. For example,
to serve resource requests with a URL pattern of /resources/** from a
public-resources directory within the web application root you would use:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/");
}
}
And the same in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/"/>
To serve these resources with a 1-year future expiration to ensure maximum use of the
browser cache and a reduction in HTTP requests made by the browser:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/").setCachePeriod(31556926);
}
}
And in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/" cache-period="31556926"/>
The mapping attribute must be an Ant pattern that can be used by
SimpleUrlHandlerMapping , and the location attribute must specify one or more valid
resource directory locations. Multiple resource locations may be specified using a
comma-separated list of values. The locations specified will be checked in the specified
order for the presence of the resource for any given request. For example, to enable the
serving of resources from both the web application root and from a known path of
/META-INF/public-web-resources/ in any jar on the classpath use:
@EnableWebMvc
@Configuration
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**")
.addResourceLocations("/", "classpath:/META-INF/public-web-resources/");
}
}
And in XML:
<mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/public-web-resources/"/>
When serving resources that may change when a new version of the application is
deployed, it is recommended that you incorporate a version string into the mapping
pattern used to request the resources, so that you may force clients to request the
newly deployed version of your application’s resources. Such a version string can be
parameterized and accessed using SpEL so that it may be easily managed in a single place
when deploying new versions.
As an example, let’s consider an application that uses a performance-optimized custom
build (as recommended) of the Dojo JavaScript library in production, and that the build
is generally deployed within the web application at a path of
/public-resources/dojo/dojo.js . Since different parts of Dojo may be incorporated into
the custom build for each new version of the application, the client web browsers need
to be forced to re-download that custom-built dojo.js resource any time a new version
of the application is deployed. A simple way to achieve this would be to manage the
version of the application in a properties file, such as:
application.version=1.0.0
and then to make the properties file’s values accessible to SpEL as a bean using the
util:properties tag:
<util:properties id="applicationProps" location="/WEB-INF/spring/application.properties"/>
With the application version now accessible via SpEL, we can incorporate this into the
use of the resources tag:
<mvc:resources mapping="/resources-#{applicationProps[application.version]}/**" location="/public-resources/"/>
In Java, you can use the @PropertySouce annotation and then inject the Environment
abstraction for access to all defined properties:
@Configuration
@EnableWebMvc
@PropertySource("/WEB-INF/spring/application.properties")
public class WebConfig extends WebMvcConfigurerAdapter {
@Inject Environment env;
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler(
"/resources-" + env.getProperty("application.version") + "/**")
.addResourceLocations("/public-resources/");
}
}
and finally, to request the resource with the proper URL, we can take advantage of the
Spring JSP tags:
<spring:eval expression="@applicationProps[application.version]" var="applicationVersion"/>
<spring:url value="/resources-{applicationVersion}" var="resourceUrl">
<spring:param name="applicationVersion" value="${applicationVersion}"/>
</spring:url>
<script src="${resourceUrl}/dojo/dojo.js" type="text/javascript"> </script>
16.16.7 Configuring Path Matching
This is a shortcut for configuring RequestMappingHandlerMapping path matching properties, without
having to override this Bean with an advanced setup.
An example of enabling pattern match features and using custom matchers, in Java:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void configurePathMatch(PathMatchConfigurer configurer) {
configurer.setUseSuffixPatternMatch(true)
.setUseTrailingSlashMatch(false)
.setPathMatcher(antPathMatcher())
.setUrlPathHelper(urlPathHelper());
}
@Bean
public UrlPathHelper urlPathHelper() {
}
@Bean
public PathMatcher antPathMatcher() {
}
}
For more details, check out the
PathMatchConfigurer API.
And the same in XML, use the <mvc:path-matching> element:
<mvc:annotation-driven>
<mvc:path-matching
suffix-pattern="true"
trailing-slash="false"
path-helper="pathHelper"
path-matcher="pathMatcher" />
</mvc:annotation-driven>
<bean id="pathHelper" class="org.example.app.MyPathHelper" />
<bean id="pathMatcher" class="org.example.app.MyPathMatcher" />
16.16.8 mvc:default-servlet-handler
This tag allows for mapping the DispatcherServlet to "/" (thus overriding the mapping
of the container’s default Servlet), while still allowing static resource requests to be
handled by the container’s default Servlet. It configures a
DefaultServletHttpRequestHandler with a URL mapping of "/**" and the lowest priority
relative to other URL mappings.
This handler will forward all requests to the default Servlet. Therefore it is important
that it remains last in the order of all other URL HandlerMappings . That will be the
case if you use <mvc:annotation-driven> or alternatively if you are setting up your
own customized HandlerMapping instance be sure to set its order property to a value
lower than that of the DefaultServletHttpRequestHandler , which is Integer.MAX_VALUE .
To enable the feature using the default setup use:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable();
}
}
Or in XML:
<mvc:default-servlet-handler/>
The caveat to overriding the "/" Servlet mapping is that the RequestDispatcher for the
default Servlet must be retrieved by name rather than by path. The
DefaultServletHttpRequestHandler will attempt to auto-detect the default Servlet for
the container at startup time, using a list of known names for most of the major Servlet
containers (including Tomcat, Jetty, GlassFish, JBoss, Resin, WebLogic, and WebSphere).
If the default Servlet has been custom configured with a different name, or if a
different Servlet container is being used where the default Servlet name is unknown,
then the default Servlet’s name must be explicitly provided as in the following example:
@Configuration
@EnableWebMvc
public class WebConfig extends WebMvcConfigurerAdapter {
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable("myCustomDefaultServlet");
}
}
Or in XML:
<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>
16.16.9 More Spring Web MVC Resources
See the following links and pointers for more resources about Spring Web MVC:
-
There are many excellent articles and tutorials that show how to build web
applications with Spring MVC. Read them at the Spring
Documentation page.
-
"Expert Spring Web MVC and Web Flow" by Seth Ladd and others (published by Apress) is
an excellent hard copy source of Spring Web MVC goodness.
16.16.10 Advanced Customizations with MVC Java Config
As you can see from the above examples, MVC Java config and the MVC namespace provide
higher level constructs that do not require deep knowledge of the underlying beans
created for you. Instead it helps you to focus on your application needs. However, at
some point you may need more fine-grained control or you may simply wish to understand
the underlying configuration.
The first step towards more fine-grained control is to see the underlying beans created
for you. In MVC Java config you can see the javadocs and the @Bean methods in
WebMvcConfigurationSupport . The configuration in this class is automatically imported
through the @EnableWebMvc annotation. In fact if you open @EnableWebMvc you can see
the @Import statement.
The next step towards more fine-grained control is to customize a property on one of the
beans created in WebMvcConfigurationSupport or perhaps to provide your own instance.
This requires two things — remove the @EnableWebMvc annotation in order to prevent
the import and then extend from DelegatingWebMvcConfiguration , a subclass of
WebMvcConfigurationSupport .
Here is an example:
@Configuration
public class WebConfig extends DelegatingWebMvcConfiguration {
@Override
public void addInterceptors(InterceptorRegistry registry){
}
@Override
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
}
}
![[Note]](images/note.png) | Note |
---|
An application should have only one configuration extending DelegatingWebMvcConfiguration
or a single @EnableWebMvc annotated class, since they both register the same underlying
beans.
Modifying beans in this way does not prevent you from using any of the higher-level
constructs shown earlier in this section. WebMvcConfigurerAdapter subclasses and
WebMvcConfigurer implementations are still being used.
|
16.16.11 Advanced Customizations with the MVC Namespace
Fine-grained control over the configuration created for you is a bit harder with the MVC
namespace.
If you do need to do that, rather than replicating the configuration it provides,
consider configuring a BeanPostProcessor that detects the bean you want to customize
by type and then modifying its properties as necessary. For example:
@Component
public class MyPostProcessor implements BeanPostProcessor {
public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {
if (bean instanceof RequestMappingHandlerAdapter) {
}
}
}
Note that MyPostProcessor needs to be included in an <component scan /> in order for
it to be detected or if you prefer you can declare it explicitly with an XML bean
declaration.
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