Heck's Blog

JAVA 代理实现
代理的实现分动态代理和静态代理，静态代理的实现是对已经生成了的JAVA类进行封装。
动态代理则是在运行时生成了相关代理类，在JAVA中生成动态代理一般有两种方式。

JDK自带实现方法
JDK实现代理生成，是用类 java.lang.reflect.Proxy, 实现方式如下

Eg:
public class JDKProxy {       public static Object getPoxyObject(final Object c) {             return Proxy.newProxyInstance(c.getClass().getClassLoader(), c.getClass().getInterfaces(),// JDK实现动态代理，但JDK实现必须需要接口                         new InvocationHandler() {                              public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {                                     Object reObj = null;                                     System.out.print("you say: ");                                     reObj = method.invoke(c, args);                                     System.out.println(" [" + Calendar.getInstance().get(Calendar.HOUR) + ":"                                                 + Calendar.getInstance().get(Calendar.MINUTE) + " "                                                 + Calendar.getInstance().get(Calendar.SECOND) + "]");                                     return reObj;                               }                         });       } }


测试代理类方法
public class TestForPoxy {       public static void main(String[] args) {             ServiceTest service = new ServiceTestImpl();             System.out.println(service.getClass().getSimpleName());             ServiceTest poxyService = (ServiceTest) JDKProxy.getPoxyObject(service);             System.out.println(poxyService.getClass().getSuperclass());             poxyService.saySomething("hello,My QQ code is 332003231.");             poxyService.saySomething("what 's your name?");             poxyService.saySomething("only for test,hehe.");       } }

1、Proxy实现代理的目标类必须有实现接口

2、 生成出来的代理类为接口实现类，和目标类不能进行转换，只能转为接口实现类进行调用

明显特点：通过此方法生成出来的类名叫做 $Proxy0

用CGLIB包实现
CGLIB是一个开源项目，官方网址是：http://cglib.sourceforge.net/，可以去上面下载最新JAR包，

本项目用的是cglib-3.0.jar

本项目还加入了依赖JAR包asm-4.0.jar，asm-util-4.0.jar

实现方式如下

Eg：
public class CGLIBProxy {       public static Object getPoxyObject(Object c) {             Enhancer enhancer = new Enhancer();             enhancer.setSuperclass(c.getClass());             enhancer.setCallback(new MethodInterceptor() {                   public Object intercept(Object arg0, Method arg1, Object[] arg2, MethodProxy proxy) throws Throwable {                         System.out.print("you say: ");                         proxy.invokeSuper(arg0, arg2);                         System.out.println(" [" + Calendar.getInstance().get(Calendar.HOUR) + ":"                                     + Calendar.getInstance().get(Calendar.MINUTE) + " " + Calendar.getInstance().get(Calendar.SECOND)                                     + "]");                         return null;                   }             });             return enhancer.create();       } }
测试代理类方法
public class TestForPoxy {       public static void main(String[] args) {             ServiceTest service = new ServiceTestImpl();             System.out.println(service.getClass().getSimpleName());          // ServiceTest poxyService = (ServiceTest) JDKProxy.getPoxyObject(service);             ServiceTest poxyService = (ServiceTest) CGLIBProxy.getPoxyObject(service);             System.out.println(poxyService.getClass().getSuperclass());             poxyService.saySomething("hello,My QQ code is 332003231.");             poxyService.saySomething("what 's your name?");             poxyService.saySomething("only for test,hehe.");       } }


1， CGLIB实现方式是对代理的目标类进行继承

2， 生成出了的代理类可以没方法，生成出来的类可以直接转换成目标类或目标类实现接口的实现类，因JAVA向上转换

明显特点：通过输出看出，看出生成出的代理类的parent类为代理的目标类



Spring  AOP的代理类机制分析


在spring中，bean都是由动态代理生成出来的，那么到底是用JDK的Proxy类实现呢，还是用CGLIB方式实现呢。

AOP  Spring需要的依赖JAR包有:

spring-asm-3.2.0.M1.jar

spring-beans-3.2.0.M1.jar

spring-context-3.2.0.M1.jar

spring-core-3.2.0.M1.jar

spring-expression-3.2.0.M1.jar

spring-aop-3.2.0.M1.jar

spring-aspects-3.2.0.M1.jar

commons\commons-logging-1.1.1\commons-logging-1.1.1.jar

aopalliance\aopalliance.jar

lib\aspectjweaver.jar



实现AOP

先简单的实现AOP
配置如下
<?xml version="1.0" encoding="utf-8"?> <beans xmlns="http://www.springframework.org/schema/beans"       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"       xsi:schemaLocation="       http://www.springframework.org/schema/beans       http://www.springframework.org/schema/beans/spring-beans-3.2.xsd       http://www.springframework.org/schema/aop     http://www.springframework.org/schema/aop/spring-aop-3.2.xsd">       <bean id="test" class="org.ben.spring.service.Test" />       <bean id="aspectBean" class="org.ben.spring.TestAspect" />       <!-- 对Test类进行AOP拦截 -->       <aop:config>             <aop:aspect id="TestAspect" ref="aspectBean">                   <!--配置切面-->                   <aop:pointcut id="businessService"                         expression="execution(* org.ben.spring.service.Test.say(..))" />                   <aop:before pointcut-ref="businessService" method="doBefore" />                   <aop:after pointcut-ref="businessService" method="doAfter" />             </aop:aspect>       </aop:config> </beans>
然后进行运行结果如下，表示AOP拦截成功

TestAspect.java
package org.ben.spring; public class TestAspect {   public void doBefore() {     System.out.println("do something in befor");   }   public void doAfter() {     System.out.println("do something in after");   } }

AOP测试类
public class TestBeans {       public static void main(String[] args) {             ApplicationContext ctx = new ClassPathXmlApplicationContext("test.xml");             Test test=(Test) ctx.getBean("test");             System.out.println(test.getClass().getSimpleName());             test.say();       } }
输出：

do something in befor

welcome for test,My QQ is 332003231

do something in after

打印代理类的生成方式


第一种情况, Test不实现任何接口，代码如下
public class Test {       public void say() {             System.out.println("welcome for test，My QQ is 332003231");       } }

在TestBeans中加入打印当前对象的名称

如下：
ApplicationContext ctx = new ClassPathXmlApplicationContext("test.xml"); Test test=(Test) ctx.getBean("test"); System.out.println(test.getClass().getSimpleName()); System.out.println("super class is "+test.getClass().getSuperclass()); test.say();
输出：

Test$$EnhancerByCGLIB$$4791b36c

super class is class org.ben.spring.service.Test

do something in befor

welcome for test,My QQ is 332003231

do something in after



明显看到用了AOP之后，输出的是代理类对象Test$$EnhancerByCGLIB$$bb9b6a7c.而且它的父类是我们的代理目标类。说明是有CGLIB生成的


第二种情况

XML的配置不变，改变代理目标类Test的实现方法，如下
public class Test implements TestInter{       public void say() {             System.out.println("welcome for test，My QQ is 332003231");       } }
和原来不同的是多继承了一个接口，接口中定义了say()方法

在TestBeans中加入打印当前对象的名称

如下：
ApplicationContext ctx = new ClassPathXmlApplicationContext("test.xml"); TestInter test=(TestInter) ctx.getBean("test"); System.out.println(test.getClass().getSimpleName()); System.out.println("super class is "+test.getClass().getSuperclass()); test.say();


输出：

$Proxy0

super class is class java.lang.reflect.Proxy

do something in befor

welcome for test,My QQ is 332003231

do something in after

结论
Spring AOP中，当拦截对象实现了接口时，生成方式是用JDK的Proxy类。当没有实现任何接口时用的是GCLIB开源项目生成的拦截类的子类.

附上本文测试的源码内容

来源：Heck's Blog
地址：https://www.heckjj.com/post/422/
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