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 {@Overridepublic 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;}@Overridepublic 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;}@Overridepublic 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;}@Overridepublic 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;}}