org.springframework.beans.factory

Interface FactoryBean<T>

All Known Subinterfaces:

SmartFactoryBean<T>

All Known Implementing Classes:

AbstractFactoryBean, AbstractServiceLoaderBasedFactoryBean, BeanReferenceFactoryBean, CommonsLogFactoryBean, FieldRetrievingFactoryBean, ListFactoryBean, MapFactoryBean, MethodInvokingFactoryBean, ObjectFactoryCreatingFactoryBean, PropertiesFactoryBean, PropertyPathFactoryBean, ProviderCreatingFactoryBean, ServiceFactoryBean, ServiceListFactoryBean, ServiceLoaderFactoryBean, ServiceLocatorFactoryBean, SetFactoryBean

public interface FactoryBean<T>

Interface to be implemented by objects used within a BeanFactory which are themselves factories. 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 references (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 SmartFactoryBean interface allows for exposing more fine-grained behavioral metadata.

This interface is heavily used within the framework itself, for example for the AOP org.springframework.aop.framework.ProxyFactoryBean or the org.springframework.jndi.JndiObjectFactoryBean. It can be used for application components as well; however, this is not common outside of infrastructure code.

NOTE: 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).

Since:

08.03.2003

Author:

Rod Johnson, Juergen Hoeller

See Also:

BeanFactory, org.springframework.aop.framework.ProxyFactoryBean, org.springframework.jndi.JndiObjectFactoryBean

Method Summary

Methods

Modifier and Type	Method and Description
T	getObject() Return an instance (possibly shared or independent) of the object managed by this factory.
Class<?>	getObjectType() Return the type of object that this FactoryBean creates, or null if not known in advance.
boolean	isSingleton() Is the object managed by this factory a singleton? That is, will getObject() always return the same object (a reference that can be cached)?

Method Detail

getObject

T getObject()
            throws Exception

Return an instance (possibly shared or independent) of the object managed by this factory.

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 FactoryBeanNotInitializedException.

As of Spring 2.0, FactoryBeans are allowed to return null 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.

Returns:

an instance of the bean (can be null)

Throws:

Exception - in case of creation errors

See Also:

FactoryBeanNotInitializedException

getObjectType

Class<?> getObjectType()

Return the type of object that this FactoryBean creates, or null if 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.

Returns:

the type of object that this FactoryBean creates, or null if not known at the time of the call

See Also:

ListableBeanFactory.getBeansOfType(java.lang.Class<T>)

isSingleton

boolean isSingleton()

Is the object managed by this factory a singleton? That is, will 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.

Returns:

whether the exposed object is a singleton

See Also:

getObject(), SmartFactoryBean.isPrototype()