Dynamic Proxy

最新推荐文章于 2024-11-13 22:00:00 发布

原创最新推荐文章于 2024-11-13 22:00:00 发布 · 386 阅读

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文章标签：

#class #object #string #equals #null #integer

本文通过示例详细解析了Java动态代理的实现原理，展示了如何利用ProxyGenerator生成代理类，并提供了具体的代码实现。

对于Dynamic Proxy的原理，很多地方都有介绍，里面最神秘的就是JVM会在运行时动态生成一个类，好奇心驱使，想看看这个生成的类的代码是啥样的。于是，跟踪到Proxy.newProxyInstance()中，发现生成代码的关键语句byte[] ProxyGenerator.generateProxyClass(String proxyname,Class[] instances)，写了段代码来输出那个类文件，并得到反编译的结果
----------IPerson .java-----------
package cn.edu.tju.bme;

public interface IPerson {

   public void insertPerson();
    public String getPersonName();
}
----------TestInvocationHandler.java-----------
package cn.edu.tju.bme;

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

public class TestInvocationHandler implements InvocationHandler {

    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        // TODO Auto-generated method stub
        return null;
    }
}
------------Main.java-----------
package cn.edu;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.InvocationHandler;

import sun.misc.ProxyGenerator;

import cn.edu.tju.bme.IPerson;
import cn.edu.tju.bme.TestInvocationHandler;

public class Main {
    public static void main(String[] args) throws IOException {
        String proxyName = "proxyName";
        InvocationHandler handler = new TestInvocationHandler();
        byte[] proxyClassFile =    ProxyGenerator.generateProxyClass( proxyName, new Class[]{IPerson.class});
        FileOutputStream fos = new FileOutputStream(new File("D://ProxyName.class"));
        fos.write(proxyClassFile);
        fos.flush();
        fos.close();
    }
}
---------------------------
反编译生成的ProxyName.class，得到的源文件如下：
----------proxyName.java-----------
import cn.edu.tju.bme.IPerson;
import java.lang.reflect.*;

public final class proxyName extends Proxy
    implements IPerson
{

    public proxyName(InvocationHandler invocationhandler)
    {
        super(invocationhandler);
    }

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

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

    public final String getPersonName ()
    {
        try
        {
            return (String)super.h.invoke(this, m4, null);
        }
        catch(Error _ex) { }
        catch(Throwable throwable)
        {
            throw new UndeclaredThrowableException(throwable);
        }
    }

    public final void insertPerson ()
    {
        try
        {
            super.h.invoke(this, m3, null);
            return;
        }
        catch(Error _ex) { }
        catch(Throwable throwable)
        {
            throw new UndeclaredThrowableException(throwable);
        }
    }

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

    private static Method m2;
    private static Method m0;
    private static Method m4;
    private static Method m3;
    private static Method m1;

    static
    {
        try
        {
            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
            m4 = Class.forName("cn.edu.tju.bme.IPerson").getMethod("getPersonName", new Class[0]);
            m3 = Class.forName("cn.edu.tju.bme.IPerson").getMethod("insertPerson", new Class[0]);
            m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] {
                Class.forName("java.lang.Object")
            });
        }
        catch(NoSuchMethodException nosuchmethodexception)
        {
            throw new NoSuchMethodError(nosuchmethodexception.getMessage());
        }