标题: Java设计模式之代理模式

创建: 2019-11-29 14:25
更新: 2019-12-02 10:51
链接: https://scz.617.cn/misc/201911291425.txt

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目录:

    1) 静态代理模式
        1.1) TicketService.java
        1.2) TicketStation.java
        1.3) TicketStationProxy.java
        1.4) TicketServiceClient.java
    2) 动态代理模式
        2.1) GeneralInvocationHandler.java
        2.2) TicketServiceClient1.java
        2.3) GeneralInvocationHandler2.java
        2.4) TicketServiceClient2.java
        2.5) TicketStation.SellTicket()调用栈回溯
        2.6) 获取动态生成的"com.sun.proxy.$Proxy0"
        2.7) 反编译动态生成的"com.sun.proxy.$Proxy0"
        2.8) 其他方案获取"com.sun.proxy.$Proxy0"
    3) 简单对比静态代理模式、动态代理模式
    4) cglib动态代理
        4.1) GeneralCglibProxy.java
        4.2) TicketServiceClient3.java
        4.3) TicketStation.SellTicket()调用栈回溯
        4.4) 获取动态生成的"TicketStation$$EnhancerByCGLIB$$abea2160"
        4.5) 反编译动态生成的类
        4.6) 其他方案获取动态生成的类
            4.6.1) GeneralCglibProxy4.java
            4.6.2) TicketServiceClient4.java
    5) 简单对比Java原生动态代理、cglib动态代理

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逆向工程中了解目标所用设计模式有助于提纲挈领。代理模式天然具有Hook能力，众
多Java框架使用代理模式。

本文没有直接展示Java动态代理技术与安全、逆向工程相关的应用方式，完全是从正
经程序员的角度提供Java动态代理技术的"Hello World"。如果你是干我这行的，我
觉得你再也找不到一篇比这篇更适合你入门的同类文章。

设计模式这种东西，还是在战争中学习战争比较有意义，照搬固定模式显得生硬，吃
不透背后的设计逻辑。程序员用程序来说话，说一千道一万，不如一套完整示例来得
简单易懂。

1) 静态代理模式

1.1) TicketService.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g TicketService.java
 *
 * 票务服务接口
 */
public interface TicketService
{
    void SellTicket ();     // 出售
    void ConsultTicket ();  // 咨询
    void ReturnTicket ();   // 退票
}
--------------------------------------------------------------------------

1.2) TicketStation.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g TicketStation.java
 */
import java.io.*;

/*
 * 售票站，具体实现票务服务接口，提供具体业务逻辑
 */
public class TicketStation implements TicketService
{
    @Override
    public void SellTicket ()
    {
        System.out.println( "TicketStation.SellTicket()" );
    }

    @Override
    public void ConsultTicket ()
    {
        System.out.println( "TicketStation.ConsultTicket()" );
    }

    @Override
    public void ReturnTicket ()
    {
        System.out.println( "TicketStation.ReturnTicket()" );
    }
}
--------------------------------------------------------------------------

1.3) TicketStationProxy.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g TicketStationProxy.java
 */
import java.io.*;

/*
 * 代理售票点，可以就近代替售票站提供便民服务。必须与售票站一样，实现票务
 * 服务接口，但有些活儿可以不自己干，转发。
 */
public class TicketStationProxy implements TicketService
{
    private TicketStation   ts;

    public TicketStationProxy ( TicketStation ts )
    {
        this.ts = ts;
    }

    @Override
    public void SellTicket ()
    {
        /*
         * 代理售票点在代理销售过程中可以提供额外服务、收取额外费用，通过
         * before()、after()体现
         */
        before( "TicketStationProxy.SellTicket()" );
        /*
         * 代理售票点转发服务请求至售票站，不需要事必躬亲，但可以自己做，
         * 比如销售假票、一票多售等等
         */
        ts.SellTicket();
        after( "TicketStationProxy.SellTicket()" );
    }

    @Override
    public void ConsultTicket ()
    {
        before( "TicketStationProxy.ConsultTicket()" );
        ts.ConsultTicket();
        after( "TicketStationProxy.ConsultTicket()" );
    }

    @Override
    public void ReturnTicket ()
    {
        before( "TicketStationProxy.ReturnTicket()" );
        ts.ReturnTicket();
        after( "TicketStationProxy.ReturnTicket()" );
    }

    private void before ( String s )
    {
        System.out.println( "Before " + s );
    }

    private void after ( String s )
    {
        System.out.println( "After " + s );
    }
}
--------------------------------------------------------------------------

1.4) TicketServiceClient.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g TicketServiceClient.java
 * java TicketServiceClient
 */
import java.io.*;

/*
 * 票务服务接口的最终用户，就是我们这些买票人
 */
public class TicketServiceClient
{
    public static void main ( String[] argv ) throws Exception
    {
        /*
         * 可以直接去售票站买票，但我们图省事，想就近在代理售票点买票
         */
        TicketStationProxy  tsp = new TicketStationProxy( new TicketStation() );
        /*
         * 调用票务服务接口的售票功能
         */
        tsp.SellTicket();
        /*
         * 调用票务服务接口的咨询功能，出事了，过年不能回湖南了，我想退票
         */
        tsp.ConsultTicket();
        /*
         * 调用票务服务接口的退票功能
         */
        tsp.ReturnTicket();
    }
}
--------------------------------------------------------------------------

$ java TicketServiceClient
Before TicketStationProxy.SellTicket()
TicketStation.SellTicket()
After TicketStationProxy.SellTicket()
Before TicketStationProxy.ConsultTicket()
TicketStation.ConsultTicket()
After TicketStationProxy.ConsultTicket()
Before TicketStationProxy.ReturnTicket()
TicketStation.ReturnTicket()
After TicketStationProxy.ReturnTicket()

有4种角色:

票务服务接口    // 定义接口
售票站          // 实现接口
代理售票点      // 实现同一接口，可转发，可自实现，可增加额外动作
买票人          // 访问接口，可以直接去售票站，也可以去代理售票点

这些设计模式噱头居多，跟传统武术套路动作差不多，我胡说的，请忽略。

2) 动态代理模式

2.1) GeneralInvocationHandler.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g GeneralInvocationHandler.java
 */
import java.io.*;
import java.lang.reflect.*;

/*
 * https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/InvocationHandler.html
 *
 * InvocationHandler is the interface implemented by the invocation
 * handler of a proxy instance. Each proxy instance has an associated
 * invocation handler. When a method is invoked on a proxy instance, the
 * method invocation is encoded and dispatched to the invoke method of its
 * invocation handler.
 */
public class GeneralInvocationHandler implements InvocationHandler
{
    private Object  realobj;

    public GeneralInvocationHandler ( Object realobj )
    {
        this.realobj    = realobj;
    }

    /*
     * This method will be invoked on an invocation handler when a method
     * is invoked on a proxy instance that it is associated with.
     */
    @Override
    public Object invoke ( Object proxy, Method method, Object[] args ) throws Throwable
    {
        /*
         * 转发至目标对象
         */
        Object  obj = method.invoke( realobj, args );
        return( obj );
    }
}
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如果看到谁把GeneralInvocationHandler这种类称为"动态代理类"，你可以喷TA一脸，
那是TA英语太差。

GeneralInvocationHandler与Ticket*没有任何静态关系，是个通用实现。因为本例
目的是演示动态代理模式的程序框架，越基本越易抓住要点。

可以让GeneralInvocationHandler与Ticket*紧耦合，在
GeneralInvocationHandler.invoke()中进行额外操作，比如before()、after()之类
的，甚至可以彻底改变预期动作，相当于把静态代理模式中TicketStationProxy的拦
截动作集中到GeneralInvocationHandler.invoke()中。

2.2) TicketServiceClient1.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g TicketServiceClient1.java
 * java TicketServiceClient1
 */
import java.io.*;
import java.lang.reflect.*;

public class TicketServiceClient1
{
    public static void main ( String[] argv ) throws Exception
    {
        GeneralInvocationHandler    gih = new GeneralInvocationHandler( new TicketStation() );
        /*
         * https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Proxy.html
         *
         * Java与C不同，后者续行用反斜杠(\)，Java不需要额外的续行符，直接
         * 折行即可。
         */
        TicketService               ts  =
        ( TicketService )Proxy.newProxyInstance
        (
            TicketService.class.getClassLoader(),
            new  Class[] { TicketService.class },
            gih
        );
        /*
         * 另一种方式得到ts，写法复杂
         */
        // ( TicketService )Proxy.
        // getProxyClass( TicketService.class.getClassLoader(), TicketService.class ).
        // getConstructor( InvocationHandler.class ).
        // newInstance( gih );
        /*
         * 就本例而言，会去调用TicketStation.SellTicket()
         */
        ts.SellTicket();
        ts.ConsultTicket();
        ts.ReturnTicket();
    }
}
--------------------------------------------------------------------------

$ java TicketServiceClient1
TicketStation.SellTicket()
TicketStation.ConsultTicket()
TicketStation.ReturnTicket()

相比静态代理模式，动态代理模式没有TicketStationProxy，但多了一个
GeneralInvocationHandler。

2.3) GeneralInvocationHandler2.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g GeneralInvocationHandler2.java
 */
import java.io.*;
import java.lang.reflect.*;

public class GeneralInvocationHandler2 implements InvocationHandler
{
    private Object  realobj;

    /*
     * 实现bind()，简化编程，参看TicketServiceClient2.java。函数名任意。
     */
    public Object bind ( Object realobj )
    {
        this.realobj    = realobj;
        Object  obj     = Proxy.newProxyInstance
        (
            realobj.getClass().getClassLoader(),
            /*
             * https://docs.oracle.com/javase/8/docs/api/java/lang/Class.html
             *
             * 返回"Class<?>[]"
             */
            realobj.getClass().getInterfaces(),
            this
        );
        return( obj );
    }

    @Override
    public Object invoke ( Object proxy, Method method, Object[] args ) throws Throwable
    {
        /*
         * 转发至目标对象
         */
        Object  obj = method.invoke( realobj, args );
        return( obj );
    }
}
--------------------------------------------------------------------------

GeneralInvocationHandler2与Ticket*同样没有任何静态关系，是个通用实现。

2.4) TicketServiceClient2.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g TicketServiceClient2.java
 * java TicketServiceClient2
 */
import java.io.*;

public class TicketServiceClient2
{
    public static void main ( String[] argv ) throws Exception
    {
        GeneralInvocationHandler2   gih = new GeneralInvocationHandler2();
        /*
         * GeneralInvocationHandler2实现bind()，简化编程
         */
        TicketService               ts  = ( TicketService )gih.bind( new TicketStation() );
        ts.SellTicket();
        ts.ConsultTicket();
        ts.ReturnTicket();
    }
}
--------------------------------------------------------------------------

TicketServiceClient2比TicketServiceClient1更简捷，进一步隐藏不必要暴露的细
节。

2.5) TicketStation.SellTicket()调用栈回溯

$ java -version
openjdk version "1.8.0_232"
OpenJDK Runtime Environment (build 1.8.0_232-b09)
OpenJDK 64-Bit Server VM (build 25.232-b09, mixed mode)

$ java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:8005,server=y,suspend=y TicketServiceClient2
$ jdb -connect com.sun.jdi.SocketAttach:hostname=127.0.0.1,port=8005

stop in TicketStation.SellTicket

  [1] TicketStation.SellTicket (TicketStation.java:14), pc = 0
  [2] sun.reflect.NativeMethodAccessorImpl.invoke0 (native method)
  [3] sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62), pc = 100
  [4] sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43), pc = 6
  [5] java.lang.reflect.Method.invoke (Method.java:498), pc = 56
  [6] GeneralInvocationHandler2.invoke (GeneralInvocationHandler2.java:37), pc = 6
  [7] com.sun.proxy.$Proxy0.SellTicket (null), pc = 9
  [8] TicketServiceClient2.main (TicketServiceClient2.java:16), pc = 24

调用栈回溯中出现一个在内存中动态生成的类:

com.sun.proxy.$Proxy0

它在设计模式中的地位相当于静态代理模式中的TicketStationProxy，但它是动态生
成的，所以这种技术方案叫动态代理模式。

TicketServiceClient2.java中的ts，其类型正是"com.sun.proxy.$Proxy0"。

查看这个类:

class com.sun.proxy.$Proxy0

    Class: com.sun.proxy.$Proxy0
    extends: java.lang.reflect.Proxy
    implements: TicketService

显示它的方法:

methods com.sun.proxy.$Proxy0

    ...
    TicketService SellTicket()
    TicketService ConsultTicket()
    TicketService ReturnTicket()

2.6) 获取动态生成的"com.sun.proxy.$Proxy0"

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g -XDignore.symbol.file TicketServiceGetTmpProxy0.java
 * java TicketServiceGetTmpProxy0 TicketServiceTmpProxy0
 *
 * warning: ProxyGenerator is internal proprietary API and may be removed in a future release
 *
 * 为了抑制这个编译时警告，Java 8可以指定"-XDignore.symbol.file"
 */
import java.io.*;
/*
 * http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/jdk8u232-ga/src/share/classes/sun/misc/ProxyGenerator.java
 */
import sun.misc.ProxyGenerator;

public class TicketServiceGetTmpProxy0
{
    private static void WriteByte
    (
        String  logname,
        /*
         * 如果是String，可以调用"somthing".getBytes()得到byte[]
         */
        byte[]  log
    )
    {
        FileOutputStream    fos;

        /*
         * 非Append模式，不存在时会自动创建
         */
        try
        {
            fos = new FileOutputStream( logname, false );
            fos.write( log );
            fos.flush();
            fos.close();
        }
        catch ( IOException e )
        {
            e.printStackTrace();
        }
    }  /* end of WriteByte */

    public static void main ( String[] argv ) throws Exception
    {
        byte[]  buf = ProxyGenerator.generateProxyClass
        (
            argv[0],
            new Class[] { TicketService.class }
        );
        WriteByte( argv[0] + ".class", buf );
    }
}
--------------------------------------------------------------------------

$ java TicketServiceGetTmpProxy0 TicketServiceTmpProxy0

在当前目录下生成TicketServiceTmpProxy0.class。TicketServiceTmpProxy0这个名
字我随便起的，可以是任意值。

2.7) 反编译动态生成的"com.sun.proxy.$Proxy0"

用JD-GUI查看TicketServiceTmpProxy0.class，对应"com.sun.proxy.$Proxy0"。

--------------------------------------------------------------------------
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class TicketServiceTmpProxy0 extends Proxy implements TicketService
{
    private static Method m4;
    private static Method m5;
    private static Method m3;

    /*
     * GeneralInvocationHandler2从此处传进来
     */
    public TicketServiceTmpProxy0 ( InvocationHandler paramInvocationHandler )
    {
        /*
         * 设置this.h
         */
        super( paramInvocationHandler );
    }

    public final void ConsultTicket ()
    {
        try
        {
            this.h.invoke( this, m4, null );
            return;
        }
        ...
    }

    public final void ReturnTicket ()
    {
        try
        {
            this.h.invoke( this, m5, null );
            return;
        }
        ...
    }

    public final void SellTicket()
    {
        try
        {
            this.h.invoke( this, m3, null );
            return;
        }
        ...
    }

    static
    {
        try
        {
            ...
            m4  = Class.forName( "TicketService" ).getMethod( "ConsultTicket", new Class[0] );
            m5  = Class.forName( "TicketService" ).getMethod( "ReturnTicket", new Class[0] );
            m3  = Class.forName( "TicketService" ).getMethod( "SellTicket", new Class[0] );
            return;
        }
        ...
    }
}
--------------------------------------------------------------------------

2.8) 其他方案获取"com.sun.proxy.$Proxy0"

http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/jdk8u232-ga/src/share/classes/sun/misc/ProxyGenerator.java

如果系统属性sun.misc.ProxyGenerator.saveGeneratedFiles为true，则内部变量
saveGeneratedFiles为true；generateProxyClass()中发现saveGeneratedFiles为
true时，会自动转储动态生成的类。下面演示另一种办法获取动态生成的
"com.sun.proxy.$Proxy0"。

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g -XDignore.symbol.file TicketServiceOtherGetTmpProxy0.java
 * mkdir -p com/sun/proxy
 * java TicketServiceOtherGetTmpProxy0 true 0
 * java TicketServiceOtherGetTmpProxy0 true 1 TicketServiceTmpProxy0
 * ls -l com/sun/proxy/
 */
import java.io.*;
import sun.misc.ProxyGenerator;

public class TicketServiceOtherGetTmpProxy0
{
    public static void main ( String[] argv ) throws Exception
    {
        /*
         * 如果argv[0]不为"true"，generateProxyClass()不会自动转储动态生成
         * 的类。
         */
        System.getProperties().put( "sun.misc.ProxyGenerator.saveGeneratedFiles", argv[0] );

        if ( argv[1].equals( "0" ) )
        {
            /*
             * 在当前目录下生成"com/sun/proxy/$Proxy0.class"，要求
             * "com/sun/proxy/"事先存在，否则报错
             */
            GeneralInvocationHandler2   gih = new GeneralInvocationHandler2();
            TicketService               ts  = ( TicketService )gih.bind( new TicketStation() );
        }
        else
        {
            /*
             * 在当前目录下生成"argv[2].class"，跟"com/sun/proxy/"没关系
             */
            byte[]  buf = ProxyGenerator.generateProxyClass
            (
                argv[2],
                new Class[] { TicketService.class }
            );
        }
    }
}
--------------------------------------------------------------------------

上例演示了多种情形，注意看注释。下面两种设置系统属性的方式等效:

System.setProperty()
System.getProperties().put()

可以用一种更简单的办法获取动态生成的"com.sun.proxy.$Proxy0":

$ java -Dsun.misc.ProxyGenerator.saveGeneratedFiles=true TicketServiceClient2
$ ls -l com/sun/proxy/
-rw-rw-r--. 1 scz scz 2179 Nov 28 17:42 $Proxy0.class

喜欢逆向工程的，记住这个方案。

3) 简单对比静态代理模式、动态代理模式

静态代理模式                动态代理模式
TicketService.java          TicketService.java
TicketStation.java          TicketStation.java
TicketStationProxy.java     com.sun.proxy.$Proxy0 and GeneralInvocationHandler2.java
TicketServiceClient.java    TicketServiceClient2.java

前两行双方都一样，重点是第三行不同。静态代理模式需要程序员自己实现
TicketStationProxy.java，动态代理模式会在运行时动态生成
com.sun.proxy.$Proxy0，同时动态代理模式需要程序员自己实现
GeneralInvocationHandler2.java。至于第四行的区别，那是自然而来的。

4) cglib动态代理

参看:

cglib
https://github.com/cglib/cglib

前面演示的动态代理是Java原生方案，有个限制，要求目标必须实现了某个接口，比
如TicketStation实现TicketService。cglib动态代理则没有这个限制，即使
TicketStation没有实现某个接口，也能拦截。外面很多cglib示例太复杂，这里继续
用TicketService、TicketStation为目标，给一个简洁示例。

4.1) GeneralCglibProxy.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g -cp cglib-nodep-3.3.0.jar GeneralCglibProxy.java
 */
import java.io.*;
import java.lang.reflect.Method;
import net.sf.cglib.proxy.*;

public class GeneralCglibProxy implements MethodInterceptor
{
    /*
     * 实现bind()，简化编程，参看TicketServiceClient3.java。函数名任意。
     */
    public Object bind ( Class<?> clazz )
    {
        Enhancer    e = new Enhancer();
        e.setSuperclass( clazz );
        e.setCallback( this );
        return( e.create() );
    }

    /*
     * 相当于GeneralInvocationHandler2.java中的invoke()，是个通用拦截点。
     */
    @Override
    public Object intercept
    (
        Object      proxy,
        Method      method,
        Object[]    args,
        MethodProxy fastMethod
    ) throws Throwable
    {
        before( "GeneralCglibProxy.intercept():" + fastMethod + "=>" + method );
        /*
         * 转发至目标对象
         */
        Object  obj = fastMethod.invokeSuper( proxy, args );
        after( "GeneralCglibProxy.intercept():" + fastMethod + "=>" + method );
        return( obj );
    }

    private void before ( String s )
    {
        System.out.println( "Before " + s );
    }

    private void after ( String s )
    {
        System.out.println( "After " + s );
    }
}
--------------------------------------------------------------------------

GeneralCglibProxy与Ticket*没有任何静态关系，是个通用实现，但可以让
GeneralCglibProxy与Ticket*紧耦合。

4.2) TicketServiceClient3.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient3.java
 * java -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient3
 */
import java.io.*;

public class TicketServiceClient3
{
    public static void main ( String[] argv ) throws Exception
    {
        /*
         * GeneralCglibProxy的相当于GeneralInvocationHandler2
         */
        GeneralCglibProxy   gcp = new GeneralCglibProxy();
        /*
         * GeneralCglibProxy实现bind()，简化编程
         */
        TicketService       ts  = ( TicketService )gcp.bind( TicketStation.class );
        ts.SellTicket();
        ts.ConsultTicket();
        ts.ReturnTicket();
    }
}
--------------------------------------------------------------------------

TicketService的存在是不必要的，代码写成这样是为了最大限度接近
TicketServiceClient2.java，更容易对比差异所在。

$ java -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient3
Before GeneralCglibProxy.intercept():net.sf.cglib.proxy.MethodProxy@5a2e4553=>public void TicketStation.SellTicket()
TicketStation.SellTicket()
After GeneralCglibProxy.intercept():net.sf.cglib.proxy.MethodProxy@5a2e4553=>public void TicketStation.SellTicket()
Before GeneralCglibProxy.intercept():net.sf.cglib.proxy.MethodProxy@7e32c033=>public void TicketStation.ConsultTicket()
TicketStation.ConsultTicket()
After GeneralCglibProxy.intercept():net.sf.cglib.proxy.MethodProxy@7e32c033=>public void TicketStation.ConsultTicket()
Before GeneralCglibProxy.intercept():net.sf.cglib.proxy.MethodProxy@7ab2bfe1=>public void TicketStation.ReturnTicket()
TicketStation.ReturnTicket()
After GeneralCglibProxy.intercept():net.sf.cglib.proxy.MethodProxy@7ab2bfe1=>public void TicketStation.ReturnTicket()

4.3) TicketStation.SellTicket()调用栈回溯

$ java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:8005,server=y,suspend=y -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient3
$ jdb -connect com.sun.jdi.SocketAttach:hostname=127.0.0.1,port=8005

stop in TicketStation.SellTicket

  [1] TicketStation.SellTicket (TicketStation.java:14), pc = 0
  [2] TicketStation$$EnhancerByCGLIB$$abea2160.CGLIB$SellTicket$0 (null), pc = 1
  [3] TicketStation$$EnhancerByCGLIB$$abea2160$$FastClassByCGLIB$$68e8c394.invoke (null), pc = 282
  [4] net.sf.cglib.proxy.MethodProxy.invokeSuper (MethodProxy.java:228), pc = 19
  [5] GeneralCglibProxy.intercept (GeneralCglibProxy.java:37), pc = 37
  [6] TicketStation$$EnhancerByCGLIB$$abea2160.SellTicket (null), pc = 31
  [7] TicketServiceClient3.main (TicketServiceClient3.java:19), pc = 19

调用栈回溯中出现几个在内存中动态生成的类:

TicketStation$$EnhancerByCGLIB$$abea2160
TicketStation$$EnhancerByCGLIB$$abea2160$$FastClassByCGLIB$$68e8c394

相当于之前讲过的"com.sun.proxy.$Proxy0"。

4.4) 获取动态生成的"TicketStation$$EnhancerByCGLIB$$abea2160"

设置系统属性"cglib.debugLocation"即可转储动态生成的类:

$ java -Dcglib.debugLocation=/tmp -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient3
$ ls -l /tmp/TicketStation*
-rw-rw-r--. 1 scz scz 5852 Nov 29 12:02 /tmp/TicketStation$$EnhancerByCGLIB$$abea2160.class
-rw-rw-r--. 1 scz scz 7177 Nov 29 12:02 /tmp/TicketStation$$EnhancerByCGLIB$$abea2160$$FastClassByCGLIB$$68e8c394.class
-rw-rw-r--. 1 scz scz 2579 Nov 29 12:02 /tmp/TicketStation$$FastClassByCGLIB$$9d2b1868.class

4.5) 反编译动态生成的类

依次反编译动态生成的三个类，其中TicketStation$$FastClassByCGLIB$$9d2b1868
是干啥的，没有深究。下文做了删减，重点关注SellTicket相关代码。

--------------------------------------------------------------------------
public class TicketStation$$EnhancerByCGLIB$$abea2160 extends TicketStation implements Factory
{
    private boolean CGLIB$BOUND;
    public static Object CGLIB$FACTORY_DATA;
    private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
    private static final Callback[] CGLIB$STATIC_CALLBACKS;
    private MethodInterceptor CGLIB$CALLBACK_0;
    private static Object CGLIB$CALLBACK_FILTER;
    private static final Method CGLIB$SellTicket$0$Method;
    private static final MethodProxy CGLIB$SellTicket$0$Proxy;
    private static final Object[] CGLIB$emptyArgs;
    private static final Method CGLIB$ReturnTicket$1$Method;
    private static final MethodProxy CGLIB$ReturnTicket$1$Proxy;
    private static final Method CGLIB$ConsultTicket$2$Method;
    private static final MethodProxy CGLIB$ConsultTicket$2$Proxy;
    private static final Method CGLIB$equals$3$Method;
    private static final MethodProxy CGLIB$equals$3$Proxy;
    private static final Method CGLIB$toString$4$Method;
    private static final MethodProxy CGLIB$toString$4$Proxy;
    private static final Method CGLIB$hashCode$5$Method;
    private static final MethodProxy CGLIB$hashCode$5$Proxy;
    private static final Method CGLIB$clone$6$Method;
    private static final MethodProxy CGLIB$clone$6$Proxy;

    static void CGLIB$STATICHOOK1() {
        final Method[] methods2 = ReflectUtils.findMethods(new String[] { "SellTicket", "()V", "ReturnTicket", "()V", "ConsultTicket", "()V" }, (forName3 = Class.forName("TicketStation")).getDeclaredMethods());
        CGLIB$SellTicket$0$Method = methods2[0];
        CGLIB$SellTicket$0$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()V", "SellTicket", "CGLIB$SellTicket$0");
        CGLIB$ReturnTicket$1$Method = methods2[1];
        CGLIB$ReturnTicket$1$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()V", "ReturnTicket", "CGLIB$ReturnTicket$1");
        CGLIB$ConsultTicket$2$Method = methods2[2];
        CGLIB$ConsultTicket$2$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()V", "ConsultTicket", "CGLIB$ConsultTicket$2");
    }

    final void CGLIB$SellTicket$0() {
        /*
         * 父类是TicketStation，此处去调TicketStation.SellTicket()
         */
        super.SellTicket();
    }

    /*
     * TicketServiceClient3先调到这个位置，并不会从此函数中直接去调
     * TicketStation.SellTicket()，因为需要给GeneralCglibProxy.intercept()
     * 机会，否则怎么拦截。
     */
    public final void SellTicket() {
        MethodInterceptor cglib$CALLBACK_2;
        MethodInterceptor cglib$CALLBACK_0;
        if ((cglib$CALLBACK_0 = (cglib$CALLBACK_2 = this.CGLIB$CALLBACK_0)) == null) {
            CGLIB$BIND_CALLBACKS(this);
            cglib$CALLBACK_2 = (cglib$CALLBACK_0 = this.CGLIB$CALLBACK_0);
        }
        if (cglib$CALLBACK_0 != null) {
            /*
             * 去调GeneralCglibProxy.intercept()
             */
            cglib$CALLBACK_2.intercept((Object)this, TicketStation$$EnhancerByCGLIB$$abea2160.CGLIB$SellTicket$0$Method, TicketStation$$EnhancerByCGLIB$$abea2160.CGLIB$emptyArgs, TicketStation$$EnhancerByCGLIB$$abea2160.CGLIB$SellTicket$0$Proxy);
            return;
        }
        super.SellTicket();
    }

    public static MethodProxy CGLIB$findMethodProxy(final Signature signature) {
        final String string = signature.toString();
        switch (string.hashCode()) {
            case -1338220137: {
                if (string.equals("SellTicket()V")) {
                    return TicketStation$$EnhancerByCGLIB$$abea2160.CGLIB$SellTicket$0$Proxy;
                }
                break;
            }
        }
        return null;
    }

    static {
        CGLIB$STATICHOOK1();
    }
}
--------------------------------------------------------------------------
public class TicketStation$$EnhancerByCGLIB$$abea2160$$FastClassByCGLIB$$68e8c394 extends FastClass
{
    public int getIndex(final Signature signature) {
        final String string = signature.toString();
        switch (string.hashCode()) {
            case -1338220137: {
                if (string.equals("SellTicket()V")) {
                    return 0;
                }
                break;
            }
            case -1126423064: {
                if (string.equals("CGLIB$SellTicket$0()V")) {
                    return 11;
                }
                break;
            }
        }
        return -1;
    }

    public int getIndex(final String s, final Class[] array) {
        Label_1255: {
            switch (s.hashCode()) {
                case 1815919902: {
                    if (!s.equals("SellTicket")) {
                        break;
                    }
                    switch (array.length) {
                        case 0: {
                            return 0;
                        }
                        default: {
                            break Label_1255;
                        }
                    }
                    break;
                }
                case 2110177901: {
                    if (!s.equals("CGLIB$SellTicket$0")) {
                        break;
                    }
                    switch (array.length) {
                        case 0: {
                            return 11;
                        }
                        default: {
                            break Label_1255;
                        }
                    }
                    break;
                }
            }
        }
        return -1;
    }

    public Object invoke(final int n, final Object o, final Object[] array) throws InvocationTargetException {
        final TicketStation$$EnhancerByCGLIB$$abea2160 ticketStation$$EnhancerByCGLIB$$abea2160 = (TicketStation$$EnhancerByCGLIB$$abea2160)o;
        try {
            switch (n) {
                case 0: {
                    ticketStation$$EnhancerByCGLIB$$abea2160.SellTicket();
                    return null;
                }
                case 11: {
                    /*
                     * 去调TicketStation$$EnhancerByCGLIB$$abea2160.CGLIB$SellTicket$0()
                     */
                    ticketStation$$EnhancerByCGLIB$$abea2160.CGLIB$SellTicket$0();
                    return null;
                }
            }
        }
    }
}
--------------------------------------------------------------------------
public class TicketStation$$FastClassByCGLIB$$9d2b1868 extends FastClass
{
    public int getIndex(final Signature signature) {
        final String string = signature.toString();
        switch (string.hashCode()) {
            case -1338220137: {
                if (string.equals("SellTicket()V")) {
                    return 0;
                }
                break;
            }
        }
        return -1;
    }

    public int getIndex(final String s, final Class[] array) {
        Label_0294: {
            switch (s.hashCode()) {
                case 1815919902: {
                    if (!s.equals("SellTicket")) {
                        break;
                    }
                    switch (array.length) {
                        case 0: {
                            return 0;
                        }
                        default: {
                            break Label_0294;
                        }
                    }
                    break;
                }
            }
        }
        return -1;
    }

    public Object invoke(final int n, final Object o, final Object[] array) throws InvocationTargetException {
        final TicketStation ticketStation = (TicketStation)o;
        try {
            switch (n) {
                case 0: {
                    ticketStation.SellTicket();
                    return null;
                }
            }
        }
    }

    public Object newInstance(final int n, final Object[] array) throws InvocationTargetException {
        try {
            switch (n) {
                case 0: {
                    return new TicketStation();
                }
            }
        }
    }
}
--------------------------------------------------------------------------

4.6) 其他方案获取动态生成的类

4.6.1) GeneralCglibProxy4.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g -cp cglib-nodep-3.3.0.jar GeneralCglibProxy4.java
 */
import java.io.*;
import java.lang.reflect.Method;
import net.sf.cglib.proxy.*;
import net.sf.cglib.core.DefaultGeneratorStrategy;

public class GeneralCglibProxy4 implements MethodInterceptor
{
    /*
     * 用于递增文件名序号
     */
    private int count   = 0;

    private void WriteByte
    (
        String  logname,
        byte[]  log
    )
    {
        FileOutputStream    fos;

        try
        {
            /*
             * 非追加模式
             */
            fos = new FileOutputStream( logname, false );
            fos.write( log );
            fos.flush();
            fos.close();
        }
        catch ( IOException e )
        {
            e.printStackTrace();
        }
    }

    public Object bind ( Class<?> clazz, String basename )
    {
        Enhancer    e = new Enhancer();
        e.setSuperclass( clazz );
        e.setCallback( this );
        if ( basename != null )
        {
            e.setStrategy
            (
                new DefaultGeneratorStrategy()
                {
                    protected byte[] transform ( byte[] b )
                    {
                        WriteByte( basename + "_" + count + ".class", b );
                        count++;
                        return( b );
                    }
                }
            );

        }
        return( e.create() );
    }

    @Override
    public Object intercept
    (
        Object      proxy,
        Method      method,
        Object[]    args,
        MethodProxy fastMethod
    ) throws Throwable
    {
        Object  obj = fastMethod.invokeSuper( proxy, args );
        return( obj );
    }
}
--------------------------------------------------------------------------

上例中transform()可以获取动态类的字节码，将之写入文件系统即可。显然此处可
以做任何动作。

4.6.2) TicketServiceClient4.java

--------------------------------------------------------------------------
/*
 * javac -encoding GBK -g -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient4.java
 * java -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient4 TicketStationTmpProxy
 */
import java.io.*;

public class TicketServiceClient4
{
    public static void main ( String[] argv ) throws Exception
    {
        GeneralCglibProxy4  gcp = new GeneralCglibProxy4();
        TicketService       ts  = ( TicketService )gcp.bind( TicketStation.class, argv[0] );
        ts.SellTicket();
        ts.ConsultTicket();
        ts.ReturnTicket();
    }
}
--------------------------------------------------------------------------

$ java -cp "cglib-nodep-3.3.0.jar:." TicketServiceClient4 TicketStationTmpProxy

将在当前目录下生成若干TicketStationTmpProxy_n.class。TicketStationTmpProxy
是我随便起的名，可以是任意值。

$ ls -l TicketStationTmpProxy*
-rw-rw-r--. 1 scz scz 5852 Nov 29 14:02 TicketStationTmpProxy_0.class
-rw-rw-r--. 1 scz scz 2579 Nov 29 14:02 TicketStationTmpProxy_1.class
-rw-rw-r--. 1 scz scz 7177 Nov 29 14:02 TicketStationTmpProxy_2.class

5) 简单对比Java原生动态代理、cglib动态代理

Java原生动态代理                cglib动态代理
TicketService.java(必要)        TicketService.java(不必要)
TicketStation.java              TicketStation.java

动态生成类                      动态生成类
com.sun.proxy.$Proxy0           TicketStation$$EnhancerByCGLIB$$abea2160
                                TicketStation$$FastClassByCGLIB$$9d2b1868
                                TicketStation$$EnhancerByCGLIB$$abea2160$$FastClassByCGLIB$$68e8c394

GeneralInvocationHandler2.java  GeneralCglibProxy.java
TicketServiceClient2.java       TicketServiceClient3.java