本文主要是介绍jdk动态代理(Proxy,InvocationHandler),含$Proxy0源码，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
转载：http://ldbjakyo.iteye.com/blog/724725
一.相关类及其方法:
java.lang.reflect.Proxy,
Proxy 提供用于创建动态代理类和实例的静态方法.
newProxyInstance()
返回一个指定接口的代理类实例，该接口可以将方法调用指派到指定的调用处理程序
(详见api文档)
java.lang.reflect.InvocationHandler,
InvocationHandler 是代理实例的调用处理程序 实现的接口。
invoke()
在代理实例上处理方法调用并返回结果。在与方法关联的代理实例上调用方法时，将在调用处理程序上调用此方法。
(详见api文档)
二.源代码:
被代理对象的接口及实现类:
package com.ml.test;public interface Manager {
public void modify();
}package com.ml.test;public class ManagerImpl implements Manager {@Override
public void modify() {System.out.println("*******modify()方法被调用");
}
}
业务代理类:
package com.ml.test;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;public class BusinessHandler implements InvocationHandler {private Object object = null;public BusinessHandler(Object object) {this.object = object;
}@Override
public Object invoke(Object proxy, Method method, Object[] args)throws Throwable {System.out.println("do something before method");Object ret = method.invoke(this.object, args);System.out.println("do something after method");return ret;}
}
客户端类:
package com.ml.test;
import java.lang.reflect.Proxy;
public class Client {public static void main(String[] args) {// 元对象(被代理对象)ManagerImpl managerImpl = new ManagerImpl();// 业务代理类BusinessHandler securityHandler = new BusinessHandler(managerImpl);// 获得代理类($Proxy0 extends Proxy implements Manager)的实例.Manager managerProxy = (Manager) Proxy.newProxyInstance(managerImpl.getClass().getClassLoader(), managerImpl.getClass().getInterfaces(), securityHandler);managerProxy.modify();
}
}
三.执行结果:
do something before method
*******modify()方法被调用
do something after method
四.机制分析:
Proxy.(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)做了以下几件事.
(1)根据参数loader和interfaces调用方法 getProxyClass(loader, interfaces)创建代理类$Proxy.
$Proxy0类实现了interfaces的接口,并继承了Proxy类.
(2)实例化$Proxy0并在构造方法中把BusinessHandler传过去,接着$Proxy0调用父类Proxy的构造器,为h赋值,如下:
class Proxy{InvocationHandler h=null;protected Proxy(InvocationHandler h) {this.h = h;}...
}
下面是本例的$Proxy0类的源码(好不容易才把它提出来,改了JRE源码,打印出字节码,把字节码保存为class文件,并反编译class文件):
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;public final class $Proxy0 extends Proxy implements Manager {private static Method m1;
private static Method m0;
private static Method m3;
private static Method m2;static {try {m1 = Class.forName("java.lang.Object").getMethod("equals",new Class[] { Class.forName("java.lang.Object") });m0 = Class.forName("java.lang.Object").getMethod("hashCode",new Class[0]);m3 = Class.forName("com.ml.test.Manager").getMethod("modify",new Class[0]);m2 = Class.forName("java.lang.Object").getMethod("toString",new Class[0]);} catch (NoSuchMethodException nosuchmethodexception) {throw new NoSuchMethodError(nosuchmethodexception.getMessage());} catch (ClassNotFoundException classnotfoundexception) {throw new NoClassDefFoundError(classnotfoundexception.getMessage());}
}public $Proxy0(InvocationHandler invocationhandler) {super(invocationhandler);
}@Override
public final boolean equals(Object obj) {try {return ((Boolean) super.h.invoke(this, m1, new Object[] { obj })).booleanValue();} catch (Throwable throwable) {throw new UndeclaredThrowableException(throwable);}
}@Override
public final int hashCode() {try {return ((Integer) super.h.invoke(this, m0, null)).intValue();} catch (Throwable throwable) {throw new UndeclaredThrowableException(throwable);}
}public final void modify() {try {super.h.invoke(this, m3, null);return;} catch (Error e) {} catch (Throwable throwable) {throw new UndeclaredThrowableException(throwable);}
}@Override
public final String toString() {try {return (String) super.h.invoke(this, m2, null);} catch (Throwable throwable) {throw new UndeclaredThrowableException(throwable);}
}
}
接着把得到的$Proxy0实例强制转换成Manager.
当执行managerProxy.modify()方法时,就调用了$Proxy0类中的modify()方法.
在modify方法中,调用父类Proxy中的h的invoke()方法.
即InvocationHandler.invoke();
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