FactoryBean which returns a value which is the result of a static or instance
method invocation. For most use cases it is better to just use the container's
built-in factory method support for the same purpose, since that is smarter at
converting arguments. This factory bean is still useful though when you need to
call a method which doesn't return any value (for example, a static class method
to force some sort of initialization to happen). This use case is not supported
by factory methods, since a return value is needed to obtain the bean instance.
Note that as it is expected to be used mostly for accessing factory methods,
this factory by default operates in a singleton fashion. The first request
to getObject() by the owning bean factory will cause a method invocation,
whose return value will be cached for subsequent requests. An internal
singleton property may be set to "false", to cause this
factory to invoke the target method each time it is asked for an object.
This invoker supports any kind of target method. A static method may be specified
by setting the targetMethod property to a String representing
the static method name, with targetClass specifying the Class
that the static method is defined on. Alternatively, a target instance method may be
specified, by setting the targetObject property as the target
object, and the targetMethod property as the name of the
method to call on that target object. Arguments for the method invocation may be
specified by setting the arguments property.
This class depends on afterPropertiesSet() being called once
all properties have been set, as per the InitializingBean contract.
An example (in an XML based bean factory definition) of a bean definition
which uses this class to call a static factory method:
Is the object managed by this factory a singleton? That is,
will FactoryBean.getObject() always return the same object
(a reference that can be cached)?
NOTE: If a FactoryBean indicates to hold a singleton object,
the object returned from getObject() might get cached
by the owning BeanFactory. Hence, do not return true
unless the FactoryBean always exposes the same reference.
The singleton status of the FactoryBean itself will generally
be provided by the owning BeanFactory; usually, it has to be
defined as singleton there.
NOTE: This method returning false does not
necessarily indicate that returned objects are independent instances.
An implementation of the extended SmartFactoryBean interface
may explicitly indicate independent instances through its
SmartFactoryBean.isPrototype() method. Plain FactoryBean
implementations which do not implement this extended interface are
simply assumed to always return independent instances if the
isSingleton() implementation returns false.
The default implementation returns true, since a
FactoryBean typically manages a singleton instance.