T- the bean type
public interface FactoryBean<T>
BeanFactorywhich are themselves factories for individual objects. If a bean implements this interface, it is used as a factory for an object to expose, not directly as a bean instance that will be exposed itself.
NB: A bean that implements this interface cannot be used as a normal bean.
A FactoryBean is defined in a bean style, but the object exposed for bean
getObject()) is always the object that it creates.
FactoryBeans can support singletons and prototypes, and can either create
objects lazily on demand or eagerly on startup. The
interface allows for exposing more fine-grained behavioral metadata.
This interface is heavily used within the framework itself, for example for
ProxyFactoryBean or the
JndiObjectFactoryBean. It can be used for
custom components as well; however, this is only common for infrastructure code.
FactoryBean is a programmatic contract. Implementations are not
supposed to rely on annotation-driven injection or other reflective facilities.
getObject() invocations may arrive early in
the bootstrap process, even ahead of any post-processor setup. If you need access
other beans, implement
BeanFactoryAware and obtain them programmatically.
Finally, FactoryBean objects participate in the containing BeanFactory's synchronization of bean creation. There is usually no need for internal synchronization other than for purposes of lazy initialization within the FactoryBean itself (or the like).
|Modifier and Type||Field and Description|
The name of an attribute that can be
|Modifier and Type||Method and Description|
Return an instance (possibly shared or independent) of the object managed by this factory.
Return the type of object that this FactoryBean creates, or
Is the object managed by this factory a singleton? That is, will
static final String OBJECT_TYPE_ATTRIBUTE
BeanDefinitionso that factory beans can signal their object type when it can't be deduced from the factory bean class.
@Nullable T getObject() throws Exception
As with a
BeanFactory, this allows support for both the
Singleton and Prototype design pattern.
If this FactoryBean is not fully initialized yet at the time of
the call (for example because it is involved in a circular reference),
throw a corresponding
As of Spring 2.0, FactoryBeans are allowed to return
objects. The factory will consider this as normal value to be used; it
will not throw a FactoryBeanNotInitializedException in this case anymore.
FactoryBean implementations are encouraged to throw
FactoryBeanNotInitializedException themselves now, as appropriate.
Exception- in case of creation errors
@Nullable Class<?> getObjectType()
nullif not known in advance.
This allows one to check for specific types of beans without instantiating objects, for example on autowiring.
In the case of implementations that are creating a singleton object, this method should try to avoid singleton creation as far as possible; it should rather estimate the type in advance. For prototypes, returning a meaningful type here is advisable too.
This method can be called before this FactoryBean has been fully initialized. It must not rely on state created during initialization; of course, it can still use such state if available.
NOTE: Autowiring will simply ignore FactoryBeans that return
null here. Therefore it is highly recommended to implement
this method properly, using the current state of the FactoryBean.
nullif not known at the time of the call
default boolean isSingleton()
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
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
may explicitly indicate independent instances through its
SmartFactoryBean.isPrototype() method. Plain
implementations which do not implement this extended interface are
simply assumed to always return independent instances if the
isSingleton() implementation returns
The default implementation returns
true, since a
FactoryBean typically manages a singleton instance.