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java动态代理

java动态代理

作者: KubiL | 来源:发表于2017-04-17 23:44 被阅读0次

    目录：

    • 简介
    • jdk动态代理
    • cglib动态代理
    • jdk动态代理与cglib的区别
    • 应用spring的aop

    简介

    动态代理是在不修改原有代码的基础上动态增强类的职责，两种实现方式，一种是jdk自带或cglib中实现的，主要应用有spring aop、记录日志、事物管理等。

    jdk动态代理

    jdk动态代理是基于java的反射机制动态生成代理类从而实现代理。
    要求：被代理类实现接口

    例子：

    Paste_Image.png 
    
public interface Subject {
    public void helloWorld();
}


    
public class RealSubject implements Subject{

    @Override
    public void helloWorld() {
        System.out.println("say hello to the world");
    }
}


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


public class MyHandler implements InvocationHandler{
    private Object target;
    public MyHandler(Object obj){
        this.target = obj;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        System.out.println("do something before");
        method.invoke(target, args);
        System.out.println("do something after");
        return null;
    }

}


    import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
public class Client {
    public static void main(String[] args) {
        RealSubject realsub = new RealSubject();
        InvocationHandler handler = new MyHandler(realsub);
        Subject sub = (Subject) Proxy.newProxyInstance(handler.getClass().getClassLoader(), 
                RealSubject.class.getInterfaces(), handler);
        sub.helloWorld();
    }
}

    网上找到反编译后的$Proxy0

    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 Subject{

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("Subject").getMethod("helloWorld",
      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 helloWorld() {
   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);
   }
}
}

    cglib动态代理

    使用cglib[Code Generation Library]实现动态代理，并不要求委托类必须实现接口，底层采用asm字节码生成框架生成代理类的字节码。
    核心：通过继承实现代理
    例子：

    public class RealSubject {
    public void helloWorld() {
        System.out.println("say hello to the world");
    }
}

    import java.lang.reflect.Method;

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class CglibProxy implements MethodInterceptor{
    public  Object createProxy(Class clazz){
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(clazz);
        enhancer.setCallback(this);
        return enhancer.create();
    }
    @Override
    public Object intercept(Object obj, Method method, Object[] args,
            MethodProxy methodProxy) throws Throwable {
        System.out.println("do before ");
        Object result = methodProxy.invokeSuper(obj, args);
        System.out.println("do after ");
        return result;
    }
    
}

    import net.sf.cglib.core.DebuggingClassWriter;

public class Client {
    public static void main(String[] args) {
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "G:\\code");
        CglibProxy  proxy = new CglibProxy();
        RealSubject proxySubject = (RealSubject) proxy.createProxy(RealSubject.class);
        proxySubject.helloWorld();
    }
}

    RealSubject$$EnhancerByCGLIB$$8f2454c.class

    import java.lang.reflect.Method;
import net.sf.cglib.core.ReflectUtils;
import net.sf.cglib.core.Signature;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class RealSubject$$EnhancerByCGLIB$$8f2454c extends RealSubject
  implements Factory
{
  private boolean CGLIB$BOUND;
  private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
  private static final Callback[] CGLIB$STATIC_CALLBACKS;
  private MethodInterceptor CGLIB$CALLBACK_0;
  private static final Method CGLIB$helloWorld$0$Method;
  private static final MethodProxy CGLIB$helloWorld$0$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 void CGLIB$STATICHOOK1()
  {
    CGLIB$THREAD_CALLBACKS = new ThreadLocal();
    CGLIB$emptyArgs = new Object[0];
    Class localClass1 = Class.forName("cglib.RealSubject$$EnhancerByCGLIB$$8f2454c");
    Class localClass2;
    Method[] tmp50_47 = ReflectUtils.findMethods(new String[] { "helloWorld", "()V" }, (localClass2 = Class.forName("cglib.RealSubject")).getDeclaredMethods());
    CGLIB$helloWorld$0$Method = tmp50_47[0];
    CGLIB$helloWorld$0$Proxy = MethodProxy.create(localClass2, localClass1, "()V", "helloWorld", "CGLIB$helloWorld$0");
    tmp50_47;
    Method[] tmp143_140 = ReflectUtils.findMethods(new String[] { "finalize", "()V", "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (localClass2 = Class.forName("java.lang.Object")).getDeclaredMethods());
    CGLIB$finalize$1$Method = tmp143_140[0];
    CGLIB$finalize$1$Proxy = MethodProxy.create(localClass2, localClass1, "()V", "finalize", "CGLIB$finalize$1");
    Method[] tmp163_143 = tmp143_140;
    CGLIB$equals$2$Method = tmp163_143[1];
    CGLIB$equals$2$Proxy = MethodProxy.create(localClass2, localClass1, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2");
    Method[] tmp183_163 = tmp163_143;
    CGLIB$toString$3$Method = tmp183_163[2];
    CGLIB$toString$3$Proxy = MethodProxy.create(localClass2, localClass1, "()Ljava/lang/String;", "toString", "CGLIB$toString$3");
    Method[] tmp203_183 = tmp183_163;
    CGLIB$hashCode$4$Method = tmp203_183[3];
    CGLIB$hashCode$4$Proxy = MethodProxy.create(localClass2, localClass1, "()I", "hashCode", "CGLIB$hashCode$4");
    Method[] tmp223_203 = tmp203_183;
    CGLIB$clone$5$Method = tmp223_203[4];
    CGLIB$clone$5$Proxy = MethodProxy.create(localClass2, localClass1, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5");
    tmp223_203;
    return;
  }

  final void CGLIB$helloWorld$0()
  {
    super.helloWorld();
  }

  public final void helloWorld()
  {
    MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
    if (tmp4_1 == null)
    {
      tmp4_1;
      CGLIB$BIND_CALLBACKS(this);
    }
    if (this.CGLIB$CALLBACK_0 != null)
      return;
    super.helloWorld();
  }

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

  protected final void finalize()
    throws Throwable
  {
    MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
    if (tmp4_1 == null)
    {
      tmp4_1;
      CGLIB$BIND_CALLBACKS(this);
    }
    if (this.CGLIB$CALLBACK_0 != null)
      return;
    super.finalize();
  }

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

  public final boolean equals(Object paramObject)
  {
    MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
    if (tmp4_1 == null)
    {
      tmp4_1;
      CGLIB$BIND_CALLBACKS(this);
    }
    MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
    if (tmp17_14 != null)
    {
      Object tmp41_36 = tmp17_14.intercept(this, CGLIB$equals$2$Method, new Object[] { paramObject }, CGLIB$equals$2$Proxy);
      tmp41_36;
      return tmp41_36 == null ? false : ((Boolean)tmp41_36).booleanValue();
    }
    return super.equals(paramObject);
  }

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

  public final String toString()
  {
    MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
    if (tmp4_1 == null)
    {
      tmp4_1;
      CGLIB$BIND_CALLBACKS(this);
    }
    MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
    if (tmp17_14 != null)
      return (String)tmp17_14.intercept(this, CGLIB$toString$3$Method, CGLIB$emptyArgs, CGLIB$toString$3$Proxy);
    return super.toString();
  }

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

  public final int hashCode()
  {
    MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
    if (tmp4_1 == null)
    {
      tmp4_1;
      CGLIB$BIND_CALLBACKS(this);
    }
    MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
    if (tmp17_14 != null)
    {
      Object tmp36_31 = tmp17_14.intercept(this, CGLIB$hashCode$4$Method, CGLIB$emptyArgs, CGLIB$hashCode$4$Proxy);
      tmp36_31;
      return tmp36_31 == null ? 0 : ((Number)tmp36_31).intValue();
    }
    return super.hashCode();
  }

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

  protected final Object clone()
    throws CloneNotSupportedException
  {
    MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
    if (tmp4_1 == null)
    {
      tmp4_1;
      CGLIB$BIND_CALLBACKS(this);
    }
    MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
    if (tmp17_14 != null)
      return tmp17_14.intercept(this, CGLIB$clone$5$Method, CGLIB$emptyArgs, CGLIB$clone$5$Proxy);
    return super.clone();
  }

  public static MethodProxy CGLIB$findMethodProxy(Signature paramSignature)
  {
    String tmp4_1 = paramSignature.toString();
    switch (tmp4_1.hashCode())
    {
    case -1574182249:
      if (tmp4_1.equals("finalize()V"))
        return CGLIB$finalize$1$Proxy;
    case -508378822:
    case 494307733:
    case 1826985398:
    case 1913648695:
    case 1984935277:
    }
  }

  public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] paramArrayOfCallback)
  {
    CGLIB$THREAD_CALLBACKS.set(paramArrayOfCallback);
  }

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

  private static final void CGLIB$BIND_CALLBACKS(Object paramObject)
  {
    // Byte code:
    //   0: aload_0
    //   1: checkcast 2 cglib/RealSubject$$EnhancerByCGLIB$$8f2454c
    //   4: astore_1
    //   5: aload_1
    //   6: getfield 198    cglib/RealSubject$$EnhancerByCGLIB$$8f2454c:CGLIB$BOUND Z
    //   9: ifne +43 -> 52
    //   12: aload_1
    //   13: iconst_1
    //   14: putfield 198   cglib/RealSubject$$EnhancerByCGLIB$$8f2454c:CGLIB$BOUND Z
    //   17: getstatic 24   cglib/RealSubject$$EnhancerByCGLIB$$8f2454c:CGLIB$THREAD_CALLBACKS  Ljava/lang/ThreadLocal;
    //   20: invokevirtual 201  java/lang/ThreadLocal:get   ()Ljava/lang/Object;
    //   23: dup
    //   24: ifnonnull +15 -> 39
    //   27: pop
    //   28: getstatic 196  cglib/RealSubject$$EnhancerByCGLIB$$8f2454c:CGLIB$STATIC_CALLBACKS  [Lnet/sf/cglib/proxy/Callback;
    //   31: dup
    //   32: ifnonnull +7 -> 39
    //   35: pop
    //   36: goto +16 -> 52
    //   39: checkcast 202  [Lnet/sf/cglib/proxy/Callback;
    //   42: aload_1
    //   43: swap
    //   44: iconst_0
    //   45: aaload
    //   46: checkcast 48   net/sf/cglib/proxy/MethodInterceptor
    //   49: putfield 36    cglib/RealSubject$$EnhancerByCGLIB$$8f2454c:CGLIB$CALLBACK_0    Lnet/sf/cglib/proxy/MethodInterceptor;
    //   52: return
  }

  public Object newInstance(Callback[] paramArrayOfCallback)
  {
    CGLIB$SET_THREAD_CALLBACKS(paramArrayOfCallback);
    CGLIB$SET_THREAD_CALLBACKS(null);
    return new 8f2454c();
  }

  public Object newInstance(Callback paramCallback)
  {
    CGLIB$SET_THREAD_CALLBACKS(new Callback[] { paramCallback });
    CGLIB$SET_THREAD_CALLBACKS(null);
    return new 8f2454c();
  }

  public Object newInstance(Class[] paramArrayOfClass, Object[] paramArrayOfObject, Callback[] paramArrayOfCallback)
  {
    CGLIB$SET_THREAD_CALLBACKS(paramArrayOfCallback);
    Class[] tmp9_8 = paramArrayOfClass;
    switch (tmp9_8.length)
    {
    case 0:
      tmp9_8;
      break;
    default:
      new 8f2454c();
      throw new IllegalArgumentException("Constructor not found");
    }
    CGLIB$SET_THREAD_CALLBACKS(null);
  }

  public Callback getCallback(int paramInt)
  {
    CGLIB$BIND_CALLBACKS(this);
    switch (paramInt)
    {
    case 0:
      break;
    }
    return null;
  }

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

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

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

  static
  {
    CGLIB$STATICHOOK1();
  }
}

    jdk动态代理与cglib的区别

    JDK动态代理
    优点
    不依赖第三方jar包, 使用方便
    随着JDK的升级，JDK动态代理的性能在稳步提升

    缺点
    只能代理实现了接口的类
    执行速度较慢

    适用场景
    如果你的程序需要频繁、反复地创建代理对象，则JDK动态代理在性能上更占优。
    cglib
    优点
    由于是动态生成字节码实现代理，因此代理对象的执行速度较快, 约为JDK动态代理的1.5 ~ 2倍
    可以代理没有实现接口的对象

    缺点
    不能代理final
    类
    动态生成字节码虽然执行较快，但是生成速度很慢，根据网上一些人的测试结果，cglib创建代理对象的速度要比JDK慢10 ~ 15倍。

    适用场景
    不需要频繁创建代理对象的应用，如spring中默认的单例bean，只需要在容器启动时生成一次代理对象。

    应用 spring aop

    被代理的类如果有实现的接口 优先使用jdk动态代理，否则用cglib动态代理。

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