学步园

知道了前面的基本知识，我们来看一下实例演示：

package danamicProxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class DynamicProxyTest {
	
	interface IHello{
		void sayHello();
	}
	
	static class Hello implements IHello{
		public void sayHello(){
			System.out.println("hello world");
		}
	}
	
	static class DynamicProxy implements InvocationHandler{
		
		Object originalObj;
		//传入被代理对象，生成代理对象
		Object bind(Object originalObj){
			this.originalObj = originalObj;
			return Proxy.newProxyInstance(originalObj.getClass().getClassLoader(),
					originalObj.getClass().getInterfaces(), this);
		}
		
		//InvocationHandler接口的方法，当代理对象调用一个方法时，就会自动转为调用次InvocationHandler对象的invoke()方法。
		@Override
		public Object invoke(Object proxy, Method method, Object[] args){
			System.out.println("welcome");
			Object obj = null;
			try {
				obj = method.invoke(originalObj, args);
			} catch (IllegalAccessException | IllegalArgumentException
					| InvocationTargetException e) {
				e.printStackTrace();
			}
			
			return obj;
		}
	}
	
	public static void main(String[] args) {
		//生成一个代理对象
		IHello hello = (IHello) new DynamicProxy().bind(new Hello());
		//通过代理对象调用被代理对象new Hello()的sayHello()方法
		hello.sayHello();
		
		//第一种方法：但是我没有找到生成的$Proxy0.class文件
		//System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
		
		//调用工具类生成$Proxy11.class文件
		ProxyGeneratorUtils.writeProxyClassToHardDisk("F:/$Proxy11.class");
	}

}

生成结果：
welcome
hello world。
其中ProxyGeneratorUtils类代码如下：

package danamicProxy;

      
    import java.io.FileOutputStream;  
    import java.io.IOException;  

import danamicProxy.DynamicProxyTest.Hello;
      
import sun.misc.ProxyGenerator;  
      
    /** 
     * 代理类的生成工具 
     
     */  
public class ProxyGeneratorUtils{  
  
    /** 
     * 把代理类的字节码写到硬盘上 
     * @param path 保存路径 
     */  
    public static void writeProxyClassToHardDisk(String path) {  
        // 第一种方法，这种方式在刚才分析ProxyGenerator时已经知道了  
        // System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", true);  
          
        // 第二种方法  
          
        // 获取代理类的字节码  
        byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy11", Hello.class.getInterfaces());  
          
        FileOutputStream out = null;  
          
        try {  
            out = new FileOutputStream(path);  
            out.write(classFile);  
            out.flush();  
        } catch (Exception e) {  
            e.printStackTrace();  
        } finally {  
            try {  
                out.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  
}

最后我们可以得到$Proxy11.class二进制文件，通过反编译，可以得到Java文件，内容如下。

// Decompiled by Jad v1.5.8e2. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://kpdus.tripod.com/jad.html
// Decompiler options: packimports(3) fieldsfirst ansi space 

import java.lang.reflect.*;

public final class $Proxy11 extends Proxy
	implements danamicProxy.DynamicProxyTest.IHello
{

	private static Method m3;
	private static Method m1;
	private static Method m0;
	private static Method m2;

	public $Proxy11(InvocationHandler invocationhandler)
	{
		super(invocationhandler);
	}

	
        //从这里我们可以看出，代理类通过实现<span class="cnblogs_code_copy"></span>danamicProxy.DynamicProxyTest.IHello<span class="cnblogs_code_copy"></span>得到了sayHello方法，
        //内部再次调用<span class="cnblogs_code_copy"></span>super.h.invoke(this, m3, null)<span class="cnblogs_code_copy"></span>，h是Proxy中保存的InvocationHandler对象
<span style="color:#FF0000;">        public final void sayHello()
	{
		try
		{
			super.h.invoke(this, m3, null);
			return;
		}
		catch (Error ) { }
		catch (Throwable throwable)
		{
			throw new UndeclaredThrowableException(throwable);
		}
	}</span>

	public final boolean equals(Object obj)
	{
		try
		{
			return ((Boolean)super.h.invoke(this, m1, new Object[] {
				obj
			})).booleanValue();
		}
		catch (Error ) { }
		catch (Throwable throwable)
		{
			throw new UndeclaredThrowableException(throwable);
		}
	}

	public final int hashCode()
	{
		try
		{
			return ((Integer)super.h.invoke(this, m0, null)).intValue();
		}
		catch (Error ) { }
		catch (Throwable throwable)
		{
			throw new UndeclaredThrowableException(throwable);
		}
	}

	public final String toString()
	{
		try
		{
			return (String)super.h.invoke(this, m2, null);
		}
		catch (Error ) { }
		catch (Throwable throwable)
		{
			throw new UndeclaredThrowableException(throwable);
		}
	}

	static 
	{
		try
		{
			m3 = Class.forName("danamicProxy.DynamicProxyTest$IHello").getMethod("sayHello", new Class[0]);
			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]);
			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());
		}
	}
}

以上就是我所理解的动态代理过程。