/*
* Copyright 2002-2007 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.config;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.util.Assert;
/**
* A {@link org.springframework.beans.factory.FactoryBean} implementation that
* returns a value which is an {@link org.springframework.beans.factory.ObjectFactory}
* that in turn returns a bean sourced from a {@link org.springframework.beans.factory.BeanFactory}.
*
* <p>As such, this may be used to avoid having a client object directly calling
* {@link org.springframework.beans.factory.BeanFactory#getBean(String)} to get
* a (typically prototype) bean from a
* {@link org.springframework.beans.factory.BeanFactory}, which would be a
* violation of the inversion of control principle. Instead, with the use
* of this class, the client object can be fed an
* {@link org.springframework.beans.factory.ObjectFactory} instance as a
* property which directly returns only the one target bean (again, which is
* typically a prototype bean).
*
* <p>A sample config in an XML-based
* {@link org.springframework.beans.factory.BeanFactory} might look as follows:
*
* <pre class="code"><beans>
*
* <!-- Prototype bean since we have state -->
* <bean id="myService" class="a.b.c.MyService" singleton="false"/>
*
* <bean id="myServiceFactory"
* class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
* <property name="targetBeanName"><idref local="myService"/></property>
* </bean>
*
* <bean id="clientBean" class="a.b.c.MyClientBean">
* <property name="myServiceFactory" ref="myServiceFactory"/>
* </bean>
*
*</beans></pre>
*
* <p>The attendant <code>MyClientBean</code> class implementation might look
* something like this:
*
* <pre class="code">package a.b.c;
*
* import org.springframework.beans.factory.ObjectFactory;
*
* public class MyClientBean {
*
* private ObjectFactory myServiceFactory;
*
* public void setMyServiceFactory(ObjectFactory myServiceFactory) {
* this.myServiceFactory = myServiceFactory;
* }
*
* public void someBusinessMethod() {
* // get a 'fresh', brand new MyService instance
* MyService service = this.myServiceFactory.getObject();
* // use the service object to effect the business logic...
* }
* }</pre>
*
* <p>An alternate approach to this application of an object creational pattern
* would be to use the {@link ServiceLocatorFactoryBean}
* to source (prototype) beans. The {@link ServiceLocatorFactoryBean} approach
* has the advantage of the fact that one doesn't have to depend on any
* Spring-specific interface such as {@link org.springframework.beans.factory.ObjectFactory},
* but has the disadvantage of requiring runtime class generation. Please do
* consult the {@link ServiceLocatorFactoryBean ServiceLocatorFactoryBean JavaDoc}
* for a fuller discussion of this issue.
*
* @author Colin Sampaleanu
* @author Juergen Hoeller
* @since 1.0.2
* @see org.springframework.beans.factory.ObjectFactory
* @see ServiceLocatorFactoryBean
*/
public class ObjectFactoryCreatingFactoryBean extends AbstractFactoryBean {
private String targetBeanName;
/**
* Set the name of the target bean.
* <p>The target does not <i>have</> to be a prototype bean, but realisticially
* always will be (because if the target bean were a singleton, then said
* singleton bean could simply be injected straight into the dependent object,
* thus obviating the need for the extra level of indirection afforded by
* the approach encapsulated by this class). Please note that no exception
* will be thrown if the supplied <code>targetBeanName</code> does not
* reference a prototype bean.
*/
public void setTargetBeanName(String targetBeanName) {
this.targetBeanName = targetBeanName;
}
public void afterPropertiesSet() throws Exception {
Assert.hasText(this.targetBeanName, "Property 'targetBeanName' is required");
super.afterPropertiesSet();
}
public Class getObjectType() {
return ObjectFactory.class;
}
protected Object createInstance() {
return new ObjectFactory() {
public Object getObject() throws BeansException {
return getTargetBean(targetBeanName);
}
};
}
/**
* Template method for obtaining a target bean instance.
* Called by the exposed ObjectFactory's <code>getObject()</code> method.
* @param targetBeanName the name of the target bean
* @return the target bean instance
*/
protected Object getTargetBean(String targetBeanName) {
return getBeanFactory().getBean(targetBeanName);
}
}