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Annotation和动态代理-2

Posted Updated
By fzsens 21 min read

为了方便表述，下面分不同的章节分别描述不同代理类的差异，最后统一进行比较

JDK Proxy

从上一篇分析中，我们已经可以得到，JDK Proxy生成的代理类为Proxy0，利用HSDB，从classes browser中可以将.class文件导出，通过procyon来进行反编译，得到内容如下

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package com.sun.proxy;

import com.qiongsong.dynamic.ProxyTester.IProxyMe;
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 ProxyTester.IProxyMe
{
  private static Method m1;
  private static Method m3;
  private static Method m2;
  private static Method m0;
  //初始化
  public $Proxy0(InvocationHandler paramInvocationHandler)
  {
    super(paramInvocationHandler);
  }
  
  static
  {
    try
    {
	  // 静态代码块，通过放射得到方法
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m3 = Class.forName("com.qiongsong.dynamic.ProxyTester$IProxyMe").getMethod("aMethod", new Class[] { Integer.TYPE });
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
      throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
    }
  }
  
  public final boolean equals(Object paramObject)
  {
    try
    {
      return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final String toString()
  {
    try
    {
      return (String)this.h.invoke(this, m2, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final int hashCode()
  {
    try
    {
      return ((Integer)this.h.invoke(this, m0, null)).intValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final void aMethod(int paramInt)
  {
    try
    {
	  // 使用代理类执行的时候，委托给h进行执行
      this.h.invoke(this, m3, new Object[] { Integer.valueOf(paramInt) });
      return;
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
}

从生成的代码中，可以很清楚看到

  1. JDK proxy生成的代码是面向接口的
  2. 静态代码块中获取对应IProxyMe接口的方法，定义为类变量
  3. 初始化的时候，会传入InvocationHandler实例，并使用父构造函数进行初始化，实际上赋值为java.lang.reflection.Proxy中的protected InvocationHandler h;变量
  4. 进行aMethod方法调用的时候，第一个参数为自己，第二个参数为静态代码块中构建的method方法，这个方法的实际拥有者是接口方法，第三个参数是将入参包装为Object[]

再看一下java.lang.reflect.Proxy.newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h)接口定义，就很容易将JDK的动态代理过程理解清楚，同时当将IProxyMe的Method和Parameter Annotation去除之后，在新输出的中jdk proxy对应的

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<<<<< ---- Invoking methods ----- >>>>>
Type: class com.qiongsong.dynamic.ProxyTester$ProxyMe_$$_jvst813_0
     Has 1  type annotation(s)
    Annotation @com.qiongsong.dynamic.ProxyTester$TypeAnnotation()
Method: aMethod
     Has 1  method annotation(s)
    Annotation @com.qiongsong.dynamic.ProxyTester$MehtodAnnotation()
    Method: aMethod has 1 parameters
        Annotations: 1
            Annotation @com.qiongsong.dynamic.ProxyTester$ParamAnnotation()
Invoked 1
-----------------
Type: class com.qiongsong.dynamic.ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c
     Has 1  type annotation(s)
    Annotation @com.qiongsong.dynamic.ProxyTester$TypeAnnotation()
Method: aMethod
     Has 1  method annotation(s)
    Annotation @com.qiongsong.dynamic.ProxyTester$MehtodAnnotation()
    Method: aMethod has 1 parameters
        Annotations: 1
            Annotation @com.qiongsong.dynamic.ProxyTester$ParamAnnotation()
Invoked 2
-----------------
Type: class com.sun.proxy.$Proxy0
     Has 0  type annotation(s)
Method: aMethod
     Has 0  method annotation(s)
    Method: aMethod has 1 parameters
        Annotations: 0
Invoked 3
-----------------
Type: class com.qiongsong.dynamic.ProxyTester$ProxyMe$ByteBuddy$NI8f8o5m
     Has 1  type annotation(s)
    Annotation @com.qiongsong.dynamic.ProxyTester$TypeAnnotation()
Method: aMethod
     Has 1  method annotation(s)
    Annotation @com.qiongsong.dynamic.ProxyTester$MehtodAnnotation()
    Method: aMethod has 1 parameters
        Annotations: 1
            Annotation @com.qiongsong.dynamic.ProxyTester$ParamAnnotation()
Invoked 4
-----------------

Method调用过程中也无法得到Annotation，因为其Method是从IProxyMe接口中获取的，而其他的代理对象，则依然可以正常获取到Annotation，可知在这块实现上各个动态代理框架的实现过程是不一样的。而Class<?>[] interfaces参数也限制了jdk proxy必须建立在接口的基础上，原因也很简单，当你extends Proxy之后，无法多重继承的Java，显然没有办法再继承代理实现类。

Cglib

也正是因为jdk proxy的必须基于接口这个特点的限制，在没有办法确定所有的对象都有接口定义的情况下，我们会选择cglib来作为动态代理框架，cglib底层采用ASM字节码生成框架，使用字节码技术生成代理类，比使用jdk proxy的执行效率更高，但是生成会稍微慢一点。使用同样的方法提取.class，使用cglib生成的的内容会比较复杂，这边不对cglib的生成原理进行介绍，主要通过生成的字节码文件，来说明整个动态代理调用的过程。

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//不同jdk proxy，cglib使用了继承实现类，并实现接口的方式，因此cglib没有必须使用接口的限制，
// 使用继承的方式，超类中标记为final的方法无法被override，因此cglib无法代理生成final方法
public class ProxyTesterProxyMeEnhancerByCGLIB9b74e96c extends ProxyTesterProxyMe implements ProxyTester$IProxyMe, Factory {
    private boolean CGLIB$BOUND;
  private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
  private static final Callback[] CGLIB$STATIC_CALLBACKS;
  private MethodInterceptor CGLIB$CALLBACK_0;
  // 可以发现每一个方法，在cglib内部都会对应一个Method和一个MethodProxy，
  // 这个MethodProxy，就是在MethodInterceptor中入口使用的MethodProxy，一般用于调用委托类(一般也就是超类)的原方法（invokeSuper），或者调用代理类(就是本类)的方法(invoke)
  // 为此MethodProxy，会生成两个独立的FastCglib代理类
  private static final Method CGLIB$aMethod$0$Method;
  private static final MethodProxy CGLIB$aMethod$0$Proxy;

  private static final Object[] CGLIB$emptyArgs;
  private static final Method CGLIB$finalize$1$Method;
  private static final MethodProxy CGLIB$finalize$1$Proxy;
  private static final Method CGLIB$equals$2$Method;
  private static final MethodProxy CGLIB$equals$2$Proxy;
  private static final Method CGLIB$toString$3$Method;
  private static final MethodProxy CGLIB$toString$3$Proxy;
  private static final Method CGLIB$hashCode$4$Method;
  private static final MethodProxy CGLIB$hashCode$4$Proxy;
  private static final Method CGLIB$clone$5$Method;
  private static final MethodProxy CGLIB$clone$5$Proxy;

  static {
      CGLIB$STATICHOOK1();
  }

  // 静态代码块，在class 加载到classloader的时候，被调用
  static void CGLIB$STATICHOOK1() {
      CGLIB$THREAD_CALLBACKS = new ThreadLocal();
      CGLIB$emptyArgs = new Object[0];
      final Class<?> forName = Class.forName("com.qiongsong.dynamic.ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c");
      final Class<?> forName2;
      // method 和 methodproxy生成
      CGLIB$aMethod$0$Method = ReflectUtils.findMethods(new String[] { "aMethod", "(I)V" }, (forName2 = Class.forName("com.qiongsong.dynamic.ProxyTester$ProxyMe")).getDeclaredMethods())[0];
      CGLIB$aMethod$0$Proxy = MethodProxy.create((Class)forName2, (Class)forName, "(I)V", "aMethod", "CGLIB$aMethod$0");

      final Class<?> forName3;
      final Method[] methods = ReflectUtils.findMethods(new String[] { "finalize", "()V", "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (forName3 = Class.forName("java.lang.Object")).getDeclaredMethods());
      CGLIB$finalize$1$Method = methods[0];
      CGLIB$finalize$1$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()V", "finalize", "CGLIB$finalize$1");
      CGLIB$equals$2$Method = methods[1];
      CGLIB$equals$2$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2");
      CGLIB$toString$3$Method = methods[2];
      CGLIB$toString$3$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()Ljava/lang/String;", "toString", "CGLIB$toString$3");
      CGLIB$hashCode$4$Method = methods[3];
      CGLIB$hashCode$4$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()I", "hashCode", "CGLIB$hashCode$4");
      CGLIB$clone$5$Method = methods[4];
      CGLIB$clone$5$Proxy = MethodProxy.create((Class)forName3, (Class)forName, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5");
  }

  // 直接调用原始方法
  final void CGLIB$aMethod$0(final int n) {
      super.aMethod(n);
  }

  // 代理方法，当我们使用代理类的时候，会调用这个方法
  public final void aMethod(final int n) {
      MethodInterceptor cglib$CALLBACK_2;
      MethodInterceptor cglib$CALLBACK_0;
      // 绑定MethodInterceptor
      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) {
          // 执行MethodInterceptor的方法，这个方法也是我们在创建cglib的时候，传入的匿名类，
          // 同样的第一个参数是 代理类自己，第二个参数，是利用放射从接口中获取到的Method，第三个参数，是封装成Object[]的参数，第四个参数，是刚才降到的MethodProxy
          cglib$CALLBACK_2.intercept((Object)this, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$aMethod$0$Method, new Object[] { new Integer(n) }, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$aMethod$0$Proxy);
          return;
      }
      super.aMethod(n);
  }

  final void CGLIB$finalize$1() throws Throwable {
      super.finalize();
  }

  protected final void finalize() throws Throwable {
      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) {
          cglib$CALLBACK_2.intercept((Object)this, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$finalize$1$Method, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$emptyArgs, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$finalize$1$Proxy);
          return;
      }
      super.finalize();
  }

  final boolean CGLIB$equals$2(final Object o) {
      return super.equals(o);
  }

  public final boolean equals(final Object o) {
      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) {
          final Object intercept = cglib$CALLBACK_2.intercept((Object)this, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$equals$2$Method, new Object[] { o }, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$equals$2$Proxy);
          return intercept != null && (boolean)intercept;
      }
      return super.equals(o);
  }

  final String CGLIB$toString$3() {
      return super.toString();
  }

  public final String toString() {
      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) {
          return (String)cglib$CALLBACK_2.intercept((Object)this, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$toString$3$Method, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$emptyArgs, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$toString$3$Proxy);
      }
      return super.toString();
  }

  final int CGLIB$hashCode$4() {
      return super.hashCode();
  }

  public final int hashCode() {
      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) {
          final Object intercept = cglib$CALLBACK_2.intercept((Object)this, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$hashCode$4$Method, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$emptyArgs, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$hashCode$4$Proxy);
          return (intercept == null) ? 0 : ((Number)intercept).intValue();
      }
      return super.hashCode();
  }

  final Object CGLIB$clone$5() throws CloneNotSupportedException {
      return super.clone();
  }

  protected final Object clone() throws CloneNotSupportedException {
      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) {
          return cglib$CALLBACK_2.intercept((Object)this, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$clone$5$Method, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$emptyArgs, ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$clone$5$Proxy);
      }
      return super.clone();
  }

  public static MethodProxy CGLIB$findMethodProxy(final Signature signature) {
      final String string = signature.toString();
      switch (string.hashCode()) {
          case -1574182249: {
              if (string.equals("finalize()V")) {
                  return ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$finalize$1$Proxy;
              }
              break;
          }
          case -1236445744: {
              if (string.equals("aMethod(I)V")) {
                  return ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$aMethod$0$Proxy;
              }
              break;
          }
          case -508378822: {
              if (string.equals("clone()Ljava/lang/Object;")) {
                  return ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$clone$5$Proxy;
              }
              break;
          }
          case 1826985398: {
              if (string.equals("equals(Ljava/lang/Object;)Z")) {
                  return ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$equals$2$Proxy;
              }
              break;
          }
          case 1913648695: {
              if (string.equals("toString()Ljava/lang/String;")) {
                  return ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$toString$3$Proxy;
              }
              break;
          }
          case 1984935277: {
              if (string.equals("hashCode()I")) {
                  return ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$hashCode$4$Proxy;
              }
              break;
          }
      }
      return null;
  }

  // 构造方法
  public ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c() {
      CGLIB$BIND_CALLBACKS(this);
  }

  public static void CGLIB$SET_THREAD_CALLBACKS(final Callback[] array) {
      ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$THREAD_CALLBACKS.set(array);
  }

  public static void CGLIB$SET_STATIC_CALLBACKS(final Callback[] cglib$STATIC_CALLBACKS) {
      CGLIB$STATIC_CALLBACKS = cglib$STATIC_CALLBACKS;
  }

  private static final void CGLIB$BIND_CALLBACKS(final Object o) {
      final ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c = (ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c)o;
      if (!proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$BOUND) {
          proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$BOUND = true;
          Object o2;
          if ((o2 = ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$THREAD_CALLBACKS.get()) != null || (o2 = ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$STATIC_CALLBACKS) != null) {
              proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])o2)[0];
          }
      }
  }

  public Object newInstance(final Callback[] array) {
      CGLIB$SET_THREAD_CALLBACKS(array);
      final ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c = new ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c();
      CGLIB$SET_THREAD_CALLBACKS(null);
      return proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c;
  }

  public Object newInstance(final Callback callback) {
      CGLIB$SET_THREAD_CALLBACKS(new Callback[] { callback });
      final ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c = new ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c();
      CGLIB$SET_THREAD_CALLBACKS(null);
      return proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c;
  }

  public Object newInstance(final Class[] array, final Object[] array2, final Callback[] array3) {
      CGLIB$SET_THREAD_CALLBACKS(array3);
      switch (array.length) {
          case 0: {
              final ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c = new ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c();
              CGLIB$SET_THREAD_CALLBACKS(null);
              return proxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c;
          }
          default: {
              throw new IllegalArgumentException("Constructor not found");
          }
      }
  }

  public Callback getCallback(final int n) {
      CGLIB$BIND_CALLBACKS(this);
      Object cglib$CALLBACK_0 = null;
      switch (n) {
          case 0: {
              cglib$CALLBACK_0 = this.CGLIB$CALLBACK_0;
              break;
          }
          default: {
              cglib$CALLBACK_0 = null;
              break;
          }
      }
      return (Callback)cglib$CALLBACK_0;
  }

  public void setCallback(final int n, final Callback callback) {
      switch (n) {
          case 0: {
              this.CGLIB$CALLBACK_0 = (MethodInterceptor)callback;
              break;
          }
      }
  }

  public Callback[] getCallbacks() {
      CGLIB$BIND_CALLBACKS(this);
      return new Callback[] { this.CGLIB$CALLBACK_0 };
  }

  public void setCallbacks(final Callback[] array) {
      this.CGLIB$CALLBACK_0 = (MethodInterceptor)array[0];
  }
}

从整体上讲，cglib的整个代理过程还是和jdk proxy比较接近的，利用高级的字节码技术，使得cglib比使用放射技术实现的jdk proxy更加灵活，在Annotation相关的操作中，因为使用了继承机制，因此cglib的类可以顺利继承TypeAnnotation，在Method和Parameter Annotation方面，则两者基本一样。在使用HSDB查看类的时候，会发现有三个类，其中ProxyTester$ProxyMe$$FastClassByCGLIB$$c2d280aa.class 和ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c$$FastClassByCGLIB$$67b37e23.class为MethodProxy自动生成的FastCglib类，前者指向代理类，后者指向委托类，也就是说，如果MethodProxy调用invokeSuper，第二个参数，需要是代理类，则会直接ProxyTester$ProxyMe$$EnhancerByCGLIB$$9b74e96c$$FastClassByCGLIB$$67b37e23.class中的CGLIB$aMethod$0(final int n)，而如果调用invoke则会根据传入的参数，调用对应的aMethod方法，如果直接调用代理类，显然会导致StackOverFlow的错误。

FastCglib的内部实现，是使用下标来标记方法，当进行调用的时候，通过方法签名获取下标，直接通过下标做直接调用，省去了反射的消耗

javassist

javassist是另一款动态字节码生成类库，它的主要特点是提供Source级别的API，可以编码的方式来生成或者修改类，而不需要对字节码有太多了解，当然也支持低级别bytecode级别的API，使用bytecode级别的api效率更高。

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//javassist的类签名和cglib类似，使用了继承的方式

public class ProxyTesterProxyMe__jvst5ab_0 extends ProxyTesterProxyMe implements ProxyObject {
  private MethodHandler handler;
  public static byte[] _filter_signature;
  public static final long serialVersionUID;
  // 存放 Method
  private static Method[] _methods_;

  public MethodHandler getHandler() {
      return this.handler;
  }

  public ProxyTester$ProxyMe_$$_jvst5ab_0() {
      this.handler = RuntimeSupport.default_interceptor;
  }

  static throws ClassNotFoundException {
      final Method[] methods_ = new Method[24];
      final Class<?> forName = Class.forName("com.qiongsong.dynamic.ProxyTester$ProxyMe_$$_jvst5ab_0");
      // 构建方法数组
      RuntimeSupport.find2Methods((Class)forName, "aMethod", "_d0aMethod", 0, "(I)V", methods_);
      RuntimeSupport.find2Methods((Class)forName, "clone", "_d1clone", 2, "()Ljava/lang/Object;", methods_);
      RuntimeSupport.find2Methods((Class)forName, "equals", "_d2equals", 4, "(Ljava/lang/Object;)Z", methods_);
      RuntimeSupport.find2Methods((Class)forName, "finalize", "_d3finalize", 6, "()V", methods_);
      RuntimeSupport.find2Methods((Class)forName, "hashCode", "_d5hashCode", 10, "()I", methods_);
      RuntimeSupport.find2Methods((Class)forName, "toString", "_d8toString", 16, "()Ljava/lang/String;", methods_);
      ProxyTester$ProxyMe_$$_jvst5ab_0._methods_ = methods_;
      serialVersionUID = 4294967295L;
  }

  protected final void finalize() throws Throwable {
      final Method[] methods_ = ProxyTester$ProxyMe_$$_jvst5ab_0._methods_;
      this.handler.invoke((Object)this, methods_[6], methods_[7], new Object[0]);
  }

  public final boolean equals(final Object o) {
      final Method[] methods_ = ProxyTester$ProxyMe_$$_jvst5ab_0._methods_;
      return (boolean)this.handler.invoke((Object)this, methods_[4], methods_[5], new Object[] { o });
  }

  public final String toString() {
      final Method[] methods_ = ProxyTester$ProxyMe_$$_jvst5ab_0._methods_;
      return (String)this.handler.invoke((Object)this, methods_[16], methods_[17], new Object[0]);
  }

  public final int hashCode() {
      final Method[] methods_ = ProxyTester$ProxyMe_$$_jvst5ab_0._methods_;
      return (int)this.handler.invoke((Object)this, methods_[10], methods_[11], new Object[0]);
  }

  protected final Object clone() throws CloneNotSupportedException {
      final Method[] methods_ = ProxyTester$ProxyMe_$$_jvst5ab_0._methods_;
      return this.handler.invoke((Object)this, methods_[2], methods_[3], new Object[0]);
  }

  Object writeReplace() throws ObjectStreamException {
      return RuntimeSupport.makeSerializedProxy((Object)this);
  }

  public final void aMethod(final int n) {
      final Method[] methods_ = ProxyTester$ProxyMe_$$_jvst5ab_0._methods_;
      // 调用的方法参数，第一个参数为代理类，第二个参数为本方法，第三个参数为原方法也就是_d0aMethod，第四个参数为构造成Object[]的参数
      this.handler.invoke((Object)this, methods_[0], methods_[1], new Object[] { new Integer(n) });
  }

  public void setHandler(final MethodHandler handler) {
      this.handler = handler;
  }

  public final void _d0aMethod(final int n) {
      super.aMethod(n);
  }

  public final Object _d1clone() throws CloneNotSupportedException {
      return super.clone();
  }

  public final boolean _d2equals(final Object o) {
      return super.equals(o);
  }

  public final void _d3finalize() throws Throwable {
      super.finalize();
  }

  public final int _d5hashCode() {
      return super.hashCode();
  }

  public final String _d8toString() {
      return super.toString();
  }
}

javassist的实现相比cglib要简单一些，RuntimeSupport.find2Methods((Class)forName, "aMethod", "_d0aMethod", 0, "(I)V", methods_);构造方法数组，

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public static void find2Methods(Class clazz, String superMethod, 
                                String thisMethod, int index,
                                String desc, java.lang.reflect.Method[] methods) {
  methods[index + 1] = thisMethod == null ? null
                                          : findMethod(clazz, thisMethod, desc);
  methods[index] = findSuperClassMethod(clazz, superMethod, desc);
}

下标index为代理类的方法，下标为index+1位继承类的对应方法，如果方法没有定义，例如接口或者abstract class ，则index+1为null。

ByteBuddy

ByteBuddy的功能和cglib类似，在官方提供的benchmark测试中，性能优于cglib等其他的工具

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public class ProxyTesterProxyMeByteBuddys1Pgctn8 extends ProxyTesterProxyMe {
  // 委托方法
  public static /* synthetic */ ProxyTester$1MyInterceptor delegate$5k4gee1;
  private static final /* synthetic */ Method cachedValue$3isHCYP0$fgups02;

  static {
    // 原方法
    cachedValue$3isHCYP0$fgups02 = ProxyTester$ProxyMe.class.getDeclaredMethod("aMethod", Integer.TYPE);
  }

  public void aMethod(final int n) {
    // 第一个参数为代理类，第二个参数为原方法，第三个参数为包装为Object的参数
    ProxyTester$ProxyMe$ByteBuddy$s1Pgctn8.delegate$5k4gee1.intercept((Object)this, ProxyTester$ProxyMe$ByteBuddy$s1Pgctn8.cachedValue$3isHCYP0$fgups02, new Object[] { n });
  }
}

ByteBuddy的生成类最为简洁，很容易就可以看得懂。

总结

动态代理的实现方式中ASM过于复杂，cglib和javassist是一般情况下是我使用动态代理的首选，jdk proxy使用了反射API，效率相比直接使用字节码较低，byteBuddy是刚刚接触了解不多。原本只是简单的Annotation继承问题，最后变成对动态代理工具的分析，稍微有点偏题了。

java
java
This post is licensed under CC BY 4.0 by the author.