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java 动态代理深度学习(Proxy,InvocationHandler),含$Proxy0源码

2012-02-28 20:48 435 查看

java 动态代理深度学习,
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):

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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