上一篇文章讲到BeanFactory，，BeanFactory是实现spring IOC原理实现的根接口，而本篇所讲的FactoryBean则是AOP原理实现的重要接口。
本文相关代码下载地址：
1. 先看FactoryBean的源码：
public interface FactoryBean<T> {T getObject() throws Exception;Class<?> getObjectType();boolean isSingleton();}2. 下面简单讲一下FactoryBean相关概念。
Spring中有两种类型的Bean，一种是普通Bean，另一种是工厂Bean，即FactoryBean，这两种Bean都被容器管理，但工厂Bean跟普通Bean不同，其返回的对象不是该factoryBean的一个实例，其返回的是该FactoryBean的getObject方法所返回的对象。如果要获取FactoryBean对象，可以在id前面加一个&符号来获取。 在Spring框架内部，有很多地方有FactoryBean的实现类，它们在很多应用如(Spring的AOP、ORM、事务管理)及与其它第三框架(ehCache)集成时都有体现。 Spring 框架中有很多FactoryBean 例如RmiProxyFactoryBean, SqlMapClientFactoryBean. LocalSessionFactoryBean等都是通过FactoryBean getObject方法驱动起来的.对bean的生产 修饰做了很好的封装。
3. 用几个例子来说明FactoryBean与普通bean的区别。
（1）普通bean
代码：
package spring.factorybean;/** * @author Ding Chengyun * 2015-2-26 */public interface PersonService {public String getName();public String sayHello();public void setName(String name);}<pre name="code" class="java">package spring.factorybean;/** * @author Ding Chengyun * 2015-2-26 */public class PersonServiceImpl implements PersonService {public String name;/* (non-Javadoc) * @see spring.PersonService#getName() */@Overridepublic String getName() {return name;}/* (non-Javadoc) * @see spring.PersonService#sayHello() */@Overridepublic String sayHello() {System.out.println("sayHello");return "sayHello";}/* (non-Javadoc) * @see spring.PersonService#setName() */@Overridepublic void setName(String name) {this.name = name;}}配置文件<bean id="personService" class="spring.factorybean.PersonServiceImpl"><property name="name"><value>hello world</value></property></bean>
测试代码：
@Testpublic void test02() {try {PersonService ps = context.getBean("personService", PersonService.class);ps.sayHello();String name = ps.getName();System.out.println(name);} catch (Exception e) {e.printStackTrace();} } （2）FactoryBean
代码：
package spring.factorybean;import org.springframework.beans.factory.FactoryBean;/** * @author Ding Chengyun * 2015-2-27 */public class MyFactoryBean implements FactoryBean<MyFactoryBeanImpl> {@Overridepublic MyFactoryBeanImpl getObject() throws Exception {return new MyFactoryBeanImpl();}@Overridepublic Class<?> getObjectType() {return MyFactoryBeanImpl.class;}@Overridepublic boolean isSingleton() {return false;}}<pre name="code" class="java">package spring.factorybean;/** * @author Ding Chengyun * 2015-2-27 */public class MyFactoryBeanImpl {}
配置文件
<bean id="myFactoryBean" class="spring.factorybean.MyFactoryBean"></bean>
测试代码：
@Testpublic void test04() {try {MyFactoryBeanImpl bean = context.getBean("myFactoryBean", MyFactoryBeanImpl.class);System.out.println(bean);MyFactoryBean factoryBean = context.getBean("&myFactoryBean", MyFactoryBean.class);System.out.println(factoryBean);bean = (MyFactoryBeanImpl) factoryBean.getObject();System.out.println(bean); } catch (Exception e) {e.printStackTrace();} }
4. 自定义一个FactoryBean，用来代理一个对象，对该对象的所有方法做一个拦截，在方法调用前后都输出一行log.
代码：
package spring.factorybean;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import org.springframework.beans.factory.DisposableBean;import org.springframework.beans.factory.FactoryBean;import org.springframework.beans.factory.InitializingBean;/** * @author Ding Chengyun * 2015-2-27 */public class MyLogFactoryBean implements FactoryBean<Object>, InitializingBean,DisposableBean {// 被代理对象实现的接口名（在使用Proxy时需要用到，用于决定生成的代理对象类型）private String interfaceName;// 被代理的对象private Object target;// 生成的代理对象private Object proxyObj;@Overridepublic void destroy() throws Exception { System.out.println("distory…"); }@Overridepublic void afterPropertiesSet() throws Exception {proxyObj = Proxy.newProxyInstance(this.getClass().getClassLoader(),new Class[] { Class.forName(interfaceName) },new InvocationHandler() {public Object invoke(Object proxy, Method method,Object[] args) throws Throwable {System.out.println("method:" + method.getName());System.out.println("Method before…");Object result = method.invoke(target, args);System.out.println("Method after…");return result;}});}@Overridepublic Object getObject() throws Exception {return proxyObj; }@Overridepublic Class<?> getObjectType() {return proxyObj == null ? Object.class : proxyObj.getClass(); }@Overridepublic boolean isSingleton() {return false;}public String getInterfaceName() {return interfaceName;}public void setInterfaceName(String interfaceName) {this.interfaceName = interfaceName;}public Object getTarget() {return target;}public void setTarget(Object target) {this.target = target;} }配置文件<bean id="myLogFactoryBean" class="spring.factorybean.MyLogFactoryBean"><property name="interfaceName" value="spring.factorybean.PersonService" /><property name="target" ref="personService"/></bean>测试代码： @Testpublic void test05() {PersonService ps = context.getBean("myLogFactoryBean", PersonService.class);ps.sayHello();//String name = ps.getName();//System.out.println(name);}
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