jdk动态代理(Proxy,InvocationHandler),含$Proxy0源码

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:
Java代码  收藏代码

  

1. package com.ml.test;  
   2.   
   3. public interface Manager {  
   4. public void modify();  
   5. }  
   6.   
   7. package com.ml.test;  
   8.   
   9. public class ManagerImpl implements Manager {  
  10.   
  11. @Override  
  12. public void modify() {  
  13.    System.out.println("*******modify()方法被调用");  
  14. }  
  15. }  

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:
Java代码  收藏代码

 

 1. package com.ml.test;  
   2.   
   3. import java.lang.reflect.InvocationHandler;  
   4. import java.lang.reflect.Method;  
   5.   
   6. public class BusinessHandler implements InvocationHandler {  
   7.   
   8. private Object object = null;  
   9.   
  10. public BusinessHandler(Object object) {  
  11.    this.object = object;  
  12. }  
  13.   
  14. @Override  
  15. public Object invoke(Object proxy, Method method, Object[] args)  
  16.     throws Throwable {  
  17.    System.out.println("do something before method");  
  18.    Object ret = method.invoke(this.object, args);  
  19.    System.out.println("do something after method");  
  20.    return ret;  
  21.   
  22. }  
  23. }  

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:
Java代码  收藏代码

  

1. package com.ml.test;  
   2. import java.lang.reflect.Proxy;  
   3. public class Client {  
   4.   
   5. public static void main(String[] args) {  
   6.    // 元对象(被代理对象)  
   7.    ManagerImpl managerImpl = new ManagerImpl();  
   8.   
   9.    // 业务代理类  
  10.    BusinessHandler securityHandler = new BusinessHandler(managerImpl);  
  11.   
  12.    // 获得代理类($Proxy0 extends Proxy implements Manager)的实例.  
  13.    Manager managerProxy = (Manager) Proxy.newProxyInstance(managerImpl  
  14.      .getClass().getClassLoader(), managerImpl.getClass()  
  15.      .getInterfaces(), securityHandler);  
  16.   
  17.    managerProxy.modify();  
  18. }  
  19. }  

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:
Java代码  收藏代码

 

 1. class Proxy{  
   2.    InvocationHandler h=null;  
   3.    protected Proxy(InvocationHandler h) {  
   4.     this.h = h;  
   5.    }  
   6.    ...  
   7. }  

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):


Java代码  收藏代码

   1. import java.lang.reflect.InvocationHandler; 
   2. import java.lang.reflect.Method; 
   3. import java.lang.reflect.Proxy; 
   4. import java.lang.reflect.UndeclaredThrowableException; 
   5.  
   6. public final class $Proxy0 extends Proxy implements Manager { 
   7.  
   8. private static Method m1; 
   9. private static Method m0; 
  10. private static Method m3; 
  11. private static Method m2; 
  12.  
  13. static { 
  14.    try { 
  15.     m1 = Class.forName("java.lang.Object").getMethod("equals", 
  16.       new Class[] { Class.forName("java.lang.Object") }); 
  17.     m0 = Class.forName("java.lang.Object").getMethod("hashCode", 
  18.       new Class[0]); 
  19.     m3 = Class.forName("com.ml.test.Manager").getMethod("modify", 
  20.       new Class[0]); 
  21.     m2 = Class.forName("java.lang.Object").getMethod("toString", 
  22.       new Class[0]); 
  23.    } catch (NoSuchMethodException nosuchmethodexception) { 
  24.     throw new NoSuchMethodError(nosuchmethodexception.getMessage()); 
  25.    } catch (ClassNotFoundException classnotfoundexception) { 
  26.     throw new NoClassDefFoundError(classnotfoundexception.getMessage()); 
  27.    } 
  28. } 
  29.  
  30. public $Proxy0(InvocationHandler invocationhandler) { 
  31.    super(invocationhandler); 
  32. } 
  33.  
  34. @Override 
  35. public final boolean equals(Object obj) { 
  36.    try { 
  37.     return ((Boolean) super.h.invoke(this, m1, new Object[] { obj })) 
  38.       .booleanValue(); 
  39.    } catch (Throwable throwable) { 
  40.     throw new UndeclaredThrowableException(throwable); 
  41.    } 
  42. } 
  43.  
  44. @Override 
  45. public final int hashCode() { 
  46.    try { 
  47.     return ((Integer) super.h.invoke(this, m0, null)).intValue(); 
  48.    } catch (Throwable throwable) { 
  49.     throw new UndeclaredThrowableException(throwable); 
  50.    } 
  51. } 
  52.  
  53. public final void modify() { 
  54.    try { 
  55.     super.h.invoke(this, m3, null); 
  56.     return; 
  57.    } catch (Error e) { 
  58.    } catch (Throwable throwable) { 
  59.     throw new UndeclaredThrowableException(throwable); 
  60.    } 
  61. } 
  62.  
  63. @Override 
  64. public final String toString() { 
  65.    try { 
  66.     return (String) super.h.invoke(this, m2, null); 
  67.    } catch (Throwable throwable) { 
  68.     throw new UndeclaredThrowableException(throwable); 
  69.    } 
  70. } 
  71. } 

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();