JDK使用InvocationHandler和Proxy实现动态代理

 

--------------------------------------------------实现InvocationHandler接口------------------------------------

package interceptor;

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

public class LogInterceptor implements InvocationHandler{

 //被代理对象
 private Object target;

 //织入的代码
 private void beforMethod(Method method)
 {
  System.out.println(method.getName()+" start "+ new Date());
 }

 @Override
 public Object invoke(Object proxy, Method method, Object[] args)
   throws Throwable {
  //先执行织入的代码
  beforMethod(method);
  //再执行被代理类里的方法
  method.invoke(target, args);
  return null;
 }

 //-------------getter setter-----------------------------------
 public Object getTarget() {
  return target;
 }

 public void setTarget(Object target) {
  this.target = target;
 }
}

-----------------------------------------------------------dao--------------------------------------------------------------------------------

 

package dao.impl;

import dao.UserDao;
import domain.User;

public class UserDaoImpl implements UserDao {

 @Override
 public void save(User user) {
  System.out.println("start dao save");
 }

}

 

---------------------------------------------------------test-----------------------------------------------------------------------------

package test;

import java.lang.reflect.Proxy;

import interceptor.LogInterceptor;
import dao.UserDao;
import dao.impl.UserDaoImpl;
import domain.User;

public class ProxyTest {

 public static void main(String[] args) {
  //被代理对象
  UserDao userDao = new UserDaoImpl();
  //织入代码的类
  LogInterceptor li = new LogInterceptor();
  li.setTarget(userDao);
  //得到代理对象..注意这里的第一个参数 要和userDao是同一个类加载器
  //第二个参数是实现哪个接口，要和被代理实现同样的接口
  //第三个参数是织入的类，该类实现了InvocationHandle接口
  UserDao userDaoProxy = (UserDao)Proxy.newProxyInstance(userDao.getClass().getClassLoader(),
    new Class[]{UserDao.class}, li);
  userDaoProxy.save(new User());

  //代理类的名字
  System.out.println(userDaoProxy.getClass().getName());

  //其实主要实现是这样的
  /**
   * public class $proxy0 implements UserDao
   * {
   *    public void save(User user)
   *    {
   *   //先得到要执行方法
   *   Method m = getMethod();
   *   //然后把自身传给 InvocationHandler的invoke方法
   *   invoke(this,m,user);//public Object invoke(Object proxy, Method method, Object[] args)
   *    }
   * }
   */

 }
}

 

-----------------------------------------------------------------------------运行结果-------------------------------------

save start Sat Sep 10 21:39:13 CST 2011
start dao save
$Proxy0