几段代码让你明白AOP和struts2中拦截器的原理

代码是李刚老师书上的源码，有助于我们理解动态代理的原理。

Dog.java

package lee;

/*
 * @author  yeeku.H.lee [e-mail]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date: 
 */
public interface Dog
{
    public void info();

    public void run();
}

DogImpl.java

package lee;


/*
 * @author  yeeku.H.lee [e-mail]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date: 
 */
public class DogImpl implements Dog
{
    public void info()
    {
        System.out.println("我是一只猎狗");
    }
    public void run()
    {
        System.out.println("我奔跑迅速");
    }
}

package lee;

/**
 * @author  yeeku.H.lee [e-mail]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date: 
 */
public class DogIntercepter
{
	public void method1()
	{
		System.out.println("=====模拟通用方法一=====");
	}

	public void method2()
	{
		System.out.println("=====模拟通用方法二=====");
	}
}

package lee;

import java.lang.reflect.*;
/*
 * @author  yeeku.H.lee [e-mail]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date: 
 */
public class MyProxyFactory
{
    /**
     * 实例Service对象。
     * @param serviceName String
     * @return Object
     */
    public static Object getProxy(Object object)
    {
       //Dog控制类 代理的操作类
        ProxyHandler handler = new ProxyHandler();
       //把该dog实例托付给代理操作
        handler.setTarget(object);
        //第一个参数是用来创建 动态代理 的ClassLoader对象，只要该对象能访问Dog接口即可。
        //也就只要DogImpl与Dog在同一
        return Proxy.newProxyInstance(object.getClass().getClassLoader(),object.getClass().getInterfaces(),handler);
    }
} 

package lee;

import java.lang.reflect.*;
import java.util.*;
/*
 * @author  yeeku.H.lee [e-mail]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date: 
 */

public class ProxyHandler implements InvocationHandler
{
    private Object target;
	DogIntercepter di = new DogIntercepter();
    public Object invoke(Object proxy, Method method, Object[] args)throws Exception
    {
        Object result = null;
        if (method.getName().equals("info"))
        {
            di.method1();
            result =method.invoke(target, args);
            di.method2();
        }
        else
        {
            result =method.invoke(target, args);
        }
        return result;
    }
    public void setTarget(Object o)
    {
        this.target = o;
    }
}

package lee;

/*
 * @author  yeeku.H.lee [e-mail]
 * @version  1.0
 * <br>Copyright (C), 2005-2008, yeeku.H.Lee
 * <br>This program is protected by copyright laws.
 * <br>Program Name:
 * <br>Date: 
 */
public class TestDog
{
    public static void main(String[] args) 
    {
        Dog targetObject = new DogImpl();
		Dog dog = null;
        Object proxy = MyProxyFactory.getProxy(targetObject);
        if (proxy instanceof Dog)
        {
            dog = (Dog)proxy;
        }
        dog.info();
        dog.run();
    }
}