接上篇

动态代理就是在实现阶段不用关心代理谁，而在运行阶段才指定代理哪一个对象。相对来说，自己写代理类的方式就是静态代理

面向切面编程（AOP）核心就是采用了动态代理机制

public interface Subject {    //业务操作    public void doSomething(String str);}

public class RealSubject implements Subject {    //业务操作    public void doSomething(String str) {        System.out.println("do something!---->" + str);    }}

public class MyInvocationHandler implements InvocationHandler {    //被代理的对象    private Object target = null;    //通过构造函数传递一个对象    public MyInvocationHandler(Object _obj) {        this.target = _obj;    }    //代理方法    public Object invoke(Object proxy, Method method, Object[] args)            throws Throwable {        //执行被代理的方法        return method.invoke(this.target, args);    }}

public class DynamicProxy
     
       {    public static 
      
        T newProxyInstance(ClassLoader loader, Class
       [] interfaces, InvocationHandler h) {        //寻找JoinPoint连接点，AOP框架使用元数据定义        if (true) {            //执行一个前置通知            (new BeforeAdvice()).exec();        }        //执行目标，并返回结果        return (T) Proxy.newProxyInstance(loader, interfaces, h);    }}
      
     

public interface IAdvice {    //通知只有一个方法，执行即可    public void exec();}public class BeforeAdvice implements IAdvice {    public void exec() {        System.out.println("我是前置通知，我被执行了！");    }}

调用

public class Client {    public static void main(String[] args) {        //定义一个主题        Subject subject = new RealSubject();        //定义一个Handler        InvocationHandler handler = new MyInvocationHandler(subject);        //定义主题的代理        Subject proxy = DynamicProxy.newProxyInstance(subject.getClass().                getClassLoader(), subject.getClass().getInterfaces(), handler);        //代理的行为        proxy.doSomething("Finish");    }}

结果

我是前置通知，我被执行了！do something!---->Finish

拓展：

public class SubjectDynamicProxy extends DynamicProxy {    public static 
     
       T newProxyInstance(Subject subject) {        //获得ClassLoader        ClassLoader loader = subject.getClass().getClassLoader();        //获得接口数组        Class
      [] classes = subject.getClass().getInterfaces();        //获得handler        InvocationHandler handler = new MyInvocationHandler(subject);        return newProxyInstance(loader, classes, handler);    }}
     

 调用

public class Client {    public static void main(String[] args) {        //定义一个主题        Subject subject = new RealSubject();        //定义主题的代理        Subject proxy = SubjectDynamicProxy.newProxyInstance(subject);        //代理的行为        proxy.doSomething("Finish");    }}