Servlet Filter that resolves multipart requests via a MultipartResolver.
in the root web application context.
Looks up the MultipartResolver in Spring's root web application context.
Supports a "multipartResolverBeanName" filter init-param in web.xml;
the default bean name is "filterMultipartResolver".
If no MultipartResolver bean is found, this filter falls back to a default
MultipartResolver: StandardServletMultipartResolver for Servlet 3.0,
based on a multipart-config section in web.xml.
Note however that at present the Servlet specification only defines how to
enable multipart configuration on a Servlet and as a result multipart request
processing is likely not possible in a Filter unless the Servlet container
provides a workaround such as Tomcat's "allowCasualMultipartParsing" property.
MultipartResolver lookup is customizable: Override this filter's
lookupMultipartResolver method to use a custom MultipartResolver
instance, for example if not using a Spring web application context.
Note that the lookup method should not create a new MultipartResolver instance
for each call but rather return a reference to a pre-built instance.
Note: This filter is an alternative to using DispatcherServlet's
MultipartResolver support, for example for web applications with custom web views
which do not use Spring's web MVC, or for custom filters applied before a Spring MVC
DispatcherServlet (e.g. HiddenHttpMethodFilter).
In any case, this filter should not be combined with servlet-specific multipart resolution.