spring 源码解读与设计详解：3 FactoryBean

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。

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()
	 */
	@Override
	public String getName() {
		return name;
	}

	/* (non-Javadoc)
	 * @see spring.PersonService#sayHello()
	 */
	@Override
	public String sayHello() {
		System.out.println("sayHello");
		return "sayHello";
	}

	/* (non-Javadoc)
	 * @see spring.PersonService#setName()
	 */
	@Override
	public 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：

@Test
	 public 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> {

	@Override
	public MyFactoryBeanImpl getObject() throws Exception {
		return new MyFactoryBeanImpl();
	}

	@Override
	public Class<?> getObjectType() {
		return MyFactoryBeanImpl.class;
	}

	@Override
	public 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：

@Test
	 public 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;  

	@Override
	public void destroy() throws Exception {
		 System.out.println("distory...");
	}

	@Override
	public 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;
					}
				});
	}

	@Override
	public Object getObject() throws Exception {
        return proxyObj;
	}

	@Override
	public Class<?> getObjectType() {
		return proxyObj == null ? Object.class : proxyObj.getClass();
	}

	@Override
	public 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：

 @Test
	 public void test05() {
	     PersonService ps = context.getBean("myLogFactoryBean", PersonService.class);  

	     ps.sayHello();  

//	     String name = ps.getName();  

//	     System.out.println(name);
	 }