org.springframework.beans.factory.FactoryBean Maven / Gradle / Ivy
/*
* Copyright 2002-2004 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.beans.factory;
/**
* Interface to be implemented by objects used within a BeanFactory
* that are themselves factories. If a bean implements this interface,
* it is used as a factory, not directly as a bean.
*
* 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 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.
*
*
This interface is heavily used within the framework, for
* example for the AOP ProxyFactoryBean or JndiObjectFactoryBean.
* It can be used for application components, but this is not common
* outside of infrastructure code.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @since 08.03.2003
* @see org.springframework.beans.factory.BeanFactory
* @see org.springframework.aop.framework.ProxyFactoryBean
* @see org.springframework.jndi.JndiObjectFactoryBean
*/
public 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 method returns null, the factory will consider the
* FactoryBean as not fully initialized and throw a corresponding
* FactoryBeanNotInitializedException.
* @return an instance of the bean (should not be null; a null value
* will be considered as an indication of incomplete initialization)
* @throws Exception in case of creation errors
* @see FactoryBeanNotInitializedException
*/
Object getObject() throws Exception;
/**
* Return the type of object that this FactoryBean creates, or null
* if not known in advance. This allows to check for specific types
* of beans without instantiating objects, for example on autowiring.
*
For a singleton, this 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.
* @return the type of object that this FactoryBean creates,
* or null if not known at the time of the call
* @see ListableBeanFactory#getBeansOfType
*/
Class getObjectType();
/**
* Is the bean managed by this factory a singleton or a prototype?
* That is, will getObject() always return the same object?
*
The singleton status of the FactoryBean itself will generally
* be provided by the owning BeanFactory; usually, it has to be
* defined as singleton there.
* @return if this bean is a singleton
*/
boolean isSingleton();
}