一个简单 JDK 动态代理的实例

动态代理的步骤：

1. 创建一个实现了InvocationHandler接口的类，必须重写接口里的invoke（）方法。
2. 创建被代理的类和接口
3. 通过Proxy的静态方法 newProxyInsatance(ClassLoader loader,Class[] interfaces,InvocationHandler,handler)来创建一个代理
4. 通过代理来调用方法

简单的动态代理实例

package com.sean.zzzjvm;
import java.lang.reflect.InvocationHandler;

import java.lang.reflect.Method;

import java.lang.reflect.Proxy;
/**

*

@Author Sean
@Date 2017/8/20 21:43.

@Version


*/

public class DynamicProxyTest {
<span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//定义一个接口</span>
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">interface</span> <span class="hljs-title" style="box-sizing: border-box; color: #445588; font-weight: bold;">IHello</span></span>{ 
    <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">void</span> <span class="hljs-title" style="box-sizing: border-box; color: #990000; font-weight: bold;">sayHello</span><span class="hljs-params" style="box-sizing: border-box;">()</span></span>;
}

<span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//实现该接口的类</span>
<span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">static</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: #445588; font-weight: bold;">Hello</span> <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: #445588; font-weight: bold;">IHello</span></span>{ 

    <span class="hljs-annotation" style="box-sizing: border-box;">@Override</span>
    <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">public</span> <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">void</span> <span class="hljs-title" style="box-sizing: border-box; color: #990000; font-weight: bold;">sayHello</span><span class="hljs-params" style="box-sizing: border-box;">()</span> </span>{
        System.out.println(<span class="hljs-string" style="box-sizing: border-box; color: #dd1144;">"hello world"</span>);
    }
}

<span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//创建一个动态代理类，实现InvocationHandler接口</span>
<span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">static</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: #445588; font-weight: bold;">DynamicProxy</span> <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: #445588; font-weight: bold;">InvocationHandler</span></span>{ 
    Object originalObj;
    
    <span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//创建一个代理的方法，在new DynamicProxy().bind(new Hello());执行</span>
    <span class="hljs-function" style="box-sizing: border-box;">Object <span class="hljs-title" style="box-sizing: border-box; color: #990000; font-weight: bold;">bind</span> <span class="hljs-params" style="box-sizing: border-box;">(Object originalObj)</span></span>{
        <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">this</span>.originalObj = originalObj;
        <span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//返回一个代理对象</span>
        <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">return</span> Proxy.newProxyInstance(originalObj.getClass().getClassLoader(),
                originalObj.getClass().getInterfaces(),<span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">this</span>);
    }

    <span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//默认重写的方法，在 hello.sayHello()执行</span>
    <span class="hljs-annotation" style="box-sizing: border-box;">@Override</span>
    <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">public</span> Object <span class="hljs-title" style="box-sizing: border-box; color: #990000; font-weight: bold;">invoke</span><span class="hljs-params" style="box-sizing: border-box;">(Object proxy, Method method, Object[] args)</span> <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">throws</span> Throwable </span>{
        System.out.println(<span class="hljs-string" style="box-sizing: border-box; color: #dd1144;">"welcome"</span>);
        <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">return</span> method.invoke(originalObj,args);
    }
}

<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">public</span> <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">void</span> <span class="hljs-title" style="box-sizing: border-box; color: #990000; font-weight: bold;">main</span><span class="hljs-params" style="box-sizing: border-box;">(String[] args)</span></span>{
    <span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">// IHello hello = new Hello();</span>
    <span class="hljs-comment" style="box-sizing: border-box; color: #999988; font-style: italic;">//调用动态代理的方法</span>
     IHello hello = (IHello) <span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">new</span> DynamicProxy().bind(<span class="hljs-keyword" style="box-sizing: border-box; color: #333333; font-weight: bold;">new</span> Hello());
    hello.sayHello();
}

}