Spring Framework

org.springframework.beans.factory.config
Class BeanReferenceFactoryBean

java.lang.Object
  extended by org.springframework.beans.factory.config.BeanReferenceFactoryBean
All Implemented Interfaces:
Aware, BeanFactoryAware, FactoryBean, SmartFactoryBean

public class BeanReferenceFactoryBean
extends java.lang.Object
implements SmartFactoryBean, BeanFactoryAware

FactoryBean that exposes an arbitrary target bean under a different name.

Usually, the target bean will reside in a different bean definition file, using this FactoryBean to link it in and expose it under a different name. Effectively, this corresponds to an alias for the target bean.

NOTE: For XML bean definition files, an <alias> tag is available that effectively achieves the same.

A special capability of this FactoryBean is enabled through its configuration as bean definition: The "targetBeanName" can be substituted through a placeholder, in combination with Spring's PropertyPlaceholderConfigurer. Thanks to Marcus Bristav for pointing this out!

Since:
1.2
Author:
Juergen Hoeller
See Also:
setTargetBeanName(java.lang.String), PropertyPlaceholderConfigurer

Constructor Summary
BeanReferenceFactoryBean()
           
 
Method Summary
 java.lang.Object getObject()
          Return an instance (possibly shared or independent) of the object managed by this factory.
 java.lang.Class getObjectType()
          Return the type of object that this FactoryBean creates, or null if not known in advance.
 boolean isEagerInit()
          Does this FactoryBean expect eager initialization, that is, eagerly initialize itself as well as expect eager initialization of its singleton object (if any)?
 boolean isPrototype()
          Is the object managed by this factory a prototype? That is, will FactoryBean.getObject() always return an independent instance?
 boolean isSingleton()
          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)?
 void setBeanFactory(BeanFactory beanFactory)
          Callback that supplies the owning factory to a bean instance.
 void setTargetBeanName(java.lang.String targetBeanName)
          Set the name of the target bean.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

BeanReferenceFactoryBean

public BeanReferenceFactoryBean()
Method Detail

setTargetBeanName

public void setTargetBeanName(java.lang.String targetBeanName)
Set the name of the target bean.

This property is required. The value for this property can be substituted through a placeholder, in combination with Spring's PropertyPlaceholderConfigurer.

Parameters:
targetBeanName - the name of the target bean
See Also:
PropertyPlaceholderConfigurer

setBeanFactory

public void setBeanFactory(BeanFactory beanFactory)
Description copied from interface: BeanFactoryAware
Callback that supplies the owning factory to a bean instance.

Invoked after the population of normal bean properties but before an initialization callback such as InitializingBean.afterPropertiesSet() or a custom init-method.

Specified by:
setBeanFactory in interface BeanFactoryAware
Parameters:
beanFactory - owning BeanFactory (never null). The bean can immediately call methods on the factory.
See Also:
BeanInitializationException

getObject

public java.lang.Object getObject()
                           throws BeansException
Description copied from interface: FactoryBean
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.

Specified by:
getObject in interface FactoryBean
Returns:
an instance of the bean (can be null)
Throws:
BeansException
See Also:
FactoryBeanNotInitializedException

getObjectType

public java.lang.Class getObjectType()
Description copied from interface: FactoryBean
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.

Specified by:
getObjectType in interface 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)

isSingleton

public boolean isSingleton()
Description copied from interface: FactoryBean
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.

Specified by:
isSingleton in interface FactoryBean
Returns:
whether the exposed object is a singleton
See Also:
FactoryBean.getObject(), SmartFactoryBean.isPrototype()

isPrototype

public boolean isPrototype()
Description copied from interface: SmartFactoryBean
Is the object managed by this factory a prototype? That is, will FactoryBean.getObject() always return an independent instance?

The prototype status of the FactoryBean itself will generally be provided by the owning BeanFactory; usually, it has to be defined as singleton there.

This method is supposed to strictly check for independent instances; it should not return true for scoped objects or other kinds of non-singleton, non-independent objects. For this reason, this is not simply the inverted form of FactoryBean.isSingleton().

Specified by:
isPrototype in interface SmartFactoryBean
Returns:
whether the exposed object is a prototype
See Also:
FactoryBean.getObject(), FactoryBean.isSingleton()

isEagerInit

public boolean isEagerInit()
Description copied from interface: SmartFactoryBean
Does this FactoryBean expect eager initialization, that is, eagerly initialize itself as well as expect eager initialization of its singleton object (if any)?

A standard FactoryBean is not expected to initialize eagerly: Its FactoryBean.getObject() will only be called for actual access, even in case of a singleton object. Returning true from this method suggests that FactoryBean.getObject() should be called eagerly, also applying post-processors eagerly. This may make sense in case of a singleton object, in particular if post-processors expect to be applied on startup.

Specified by:
isEagerInit in interface SmartFactoryBean
Returns:
whether eager initialization applies
See Also:
ConfigurableListableBeanFactory.preInstantiateSingletons()

Spring Framework