objectfactorycreatingfactorybean.java

spring api 源代码

/*
 * 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">&lt;beans&gt;
 *
 *   &lt;!-- Prototype bean since we have state --&gt;
 *   &lt;bean id="myService" class="a.b.c.MyService" singleton="false"/&gt;
 *
 *   &lt;bean id="myServiceFactory"
 *       class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean"&gt;
 *     &lt;property name="targetBeanName"&gt;&lt;idref local="myService"/&gt;&lt;/property&gt;
 *   &lt;/bean&gt;
 *
 *   &lt;bean id="clientBean" class="a.b.c.MyClientBean"&gt;
 *     &lt;property name="myServiceFactory" ref="myServiceFactory"/&gt;
 *   &lt;/bean&gt;
 *
 *&lt;/beans&gt;</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);
	}

}