动态代理

一辆坦克，有move()方法，现在要不改变坦克类，且能加上日志。

 

package com.test.myproxy.dongtai;

public interface Moveable {
	public void move();
}

 

 

package com.test.myproxy.dongtai;

public class Tank implements Moveable {
	@Override
	public void move() {
		System.out.println("moving");
	}
	
}

 

日志代理类：

package com.test.myproxy.dongtai;

import java.lang.reflect.InvocationHandler;

public class LoggerHandler implements InvocationHandler {

	private Object obj;
	
	public LoggerHandler(Object obj) {
		super();
		this.obj = obj;
	}

	

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		System.out.println("日志开始");
		Object result = method.invoke(this.obj, args);
		System.out.println("日志结束");
		return result;
	}
	
}

 

package com.test.myproxy.dongtai;

import java.lang.reflect.InvocationHandler;

public class Client {
	public static void main(String[] args) {
		  Moveable m = new Tank();
		  InvocationHandler h = new LoggerHandler(m);
		  //InvocationHandler th = new TranstractHandler(h);
		  Moveable proxy = (Moveable)Proxy.newProxyInstance(
				  m.getClass().getClassLoader(),
				  m.getClass().getInterfaces(),
				  h);
		  proxy.move();
	}
}

 

到这里，动态代理就实现了。

 

但有个问题，我只能代理一个日志，不能在日志的方法上再包一层事物

事物代理：

package com.test.myproxy.dongtai;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class TranstractHandler implements InvocationHandler {
	private Object obj;

	public TranstractHandler(Object obj) {
		super();
		this.obj = obj;
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		System.out.println("事物开始");
		Object result = method.invoke(this.obj, args);
		System.out.println("插入日志表");
		System.out.println("事物结束");
		return result;
	}
	
}

 

 InvocationHandler th = new TranstractHandler(h);
		  Moveable proxy = (Moveable)Proxy.newProxyInstance(
				  m.getClass().getClassLoader(),
				  m.getClass().getInterfaces(),
				  th);
		  proxy.move();

 这段代码会抛 Exception in thread "main" java.lang.IllegalArgumentException: object is not an instance of declaring class

这个错误。不知道怎么改。。。

 

已找到解决办法：

package com.test.myproxy.dongtai;

import java.lang.reflect.InvocationHandler;

public class LoggerHandler implements InvocationHandler {

	private Object obj;
	
	public LoggerHandler(Object obj) {
		super();
		this.obj = obj;
	}

	

	@Override
	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		System.out.println("日志开始");
		Object result = null;
		if(this.obj instanceof InvocationHandler) {
			result = ((InvocationHandler)this.obj).invoke(proxy, method, args);
		} else {
			result = method.invoke(this.obj, args);
		}


//事物代理中同样修改
		System.out.println("日志结束");
		return result;
	}
}