[编织消息框架][JAVA核心技术]jdk动态代理

需要用到的工具  jdk : javac javap

class 反编译 ：JD-GUI http://jd.benow.ca/

先来看下jdk动态代理跟native性能比较

package com.eyu.onequeue;

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

public class TestProxy {
    public interface UserService {
    public String getName(int id);

    public Integer getAge(int id);
    }

    public static class UserServiceImpl implements UserService {

    @Override
    public String getName(int id) {
        return "name : " + id;
    }

    @Override
    public Integer getAge(int id) {
        return id;
    }
    };

    public static void main(String[] args) {
    testNative();
    testJdk();
    }

    public static void testJdk() {
    UserService impTarget = new UserServiceImpl();
    // 代理处理逻辑
    InvocationHandler handler = new InvocationHandler() {

        @Override
        public Object invoke(Object target, Method method, Object[] args) throws Throwable {
        return method.invoke(impTarget, args);
        }
    };
    // Proxy.newProxyInstance(ClassLoader/**ClassLoader 没有特别处理 拿默认即可 **/,
    // Class<?>[]/**代理接口类**/, InvocationHandler /**代理处理逻辑**/)
    UserService proxy = (UserService) Proxy.newProxyInstance(TestProxy.class.getClassLoader(), new Class[] { UserService.class }, handler);

    run("jdk", proxy);
    }

    public static void testNative() {
    UserService impTarget = new UserServiceImpl();
    run("native", impTarget);
    }

    private static void run(String tag, UserService impTarget) {
    int c = 15;
    System.out.println();
    while (c-- > 0) {
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000000; i++) {
        impTarget.getName(11);
        }
        long end = System.currentTimeMillis();
        System.out.print(tag + ": " + (end - start) + " ");
    }
    }
}

运行结果:

native: 175 native: 182 native: 126 native: 172 native: 126 native: 127 native: 127 native: 126 native: 127 native: 126 native: 126 native: 128 native: 126 native: 127 native: 126
jdk: 214 jdk: 170 jdk: 169 jdk: 169 jdk: 170 jdk: 170 jdk: 170 jdk: 170 jdk: 170 jdk: 172 jdk: 169 jdk: 172 jdk: 169 jdk: 171 jdk: 169

先运行预热，看出执行五次之后比较稳定

jdk动态代理使用非常简单，使用Proxy.newProxyInstance 静态方法即可

接下来我们看下class指令

javac -encoding UTF-8 -d . TestProxy.java

javap -v comeyuonequeueTestProxy.class > s.txt

其中

 // Method java/lang/reflect/Proxy.newProxyInstance:(Ljava/lang/ClassLoader;[Ljava/lang/Class;Ljava/lang/reflect/InvocationHandler;)Ljava/lang/Object;

没有详细看到代理类指令

运行时生成的动态代理对象是可以导出到文件的，方法有两种

1. 在代码中加入System.setProperty("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
2. 在运行时加入jvm 参数 -Dsun.misc.ProxyGenerator.saveGeneratedFiles=true

我们在main方法加一行System.setProperty("sun.misc.ProxyGenerator.saveGeneratedFiles", "true"); 然后执行一下

 public static void main(String[] args) {
    System.setProperty("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
     //省略
 }

这时在包下会多出$Proxy0.class文件

proxy0.class用jd-gui打开

package com.sun.proxy;

import com.eyu.onequeue.TestProxy.UserService;
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 TestProxy.UserService
{
  private static Method m1;
  private static Method m2;
  private static Method m3;
  private static Method m4;
  private static Method m0;
  
  public $Proxy0(InvocationHandler paramInvocationHandler)
  {
    super(paramInvocationHandler);
  }
  
  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 String getName(int paramInt)
  {
    try
    {
      return (String)this.h.invoke(this, m3, new Object[] { Integer.valueOf(paramInt) });
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  
  public final Integer getAge(int paramInt)
  {
    try
    {
      return (Integer)this.h.invoke(this, m4, new Object[] { Integer.valueOf(paramInt) });
    }
    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);
    }
  }
  
  static
  {
    try
    {
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      m3 = Class.forName("com.eyu.onequeue.TestProxy$UserService").getMethod("getName", new Class[] { Integer.TYPE });
      m4 = Class.forName("com.eyu.onequeue.TestProxy$UserService").getMethod("getAge", new Class[] { Integer.TYPE });
      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());
    }
  }
}

proxy0分析分两部份

1.在内存动态生成代理类 以$proxy 开头

$Proxy0 extends Proxy implements XXXXProxy.UserService

并初始化InvocationHandler 同绑定 Method

public $Proxy0(InvocationHandler paramInvocationHandler)
{
　　super(paramInvocationHandler);
}

static
{
try
{
　　m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
　　m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
　　m3 = Class.forName("com.eyu.onequeue.TestProxy$UserService").getMethod("getName", new Class[] { Integer.TYPE });
　　m4 = Class.forName("com.eyu.onequeue.TestProxy$UserService").getMethod("getAge", new Class[] { Integer.TYPE });
　　m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
　　return;
}
.....
}

第二部分：代理原对象所有方法实现调用InvocationHandler 类的 Object invoke(Object target, Method method, Object[] args) throws Throwable 方法 再通过method反射invoke

public final String getName(int paramInt)
{
try
{
    return (String)this.h.invoke(this, m3, new Object[] { Integer.valueOf(paramInt) });
}
catch (Error|RuntimeException localError)
{
    throw localError;
}
catch (Throwable localThrowable)
{
    throw new UndeclaredThrowableException(localThrowable);
}
}

我们通过生成指令 E:javafindmecomsunproxy>javap -v $Proxy0.class > d.txt

来查看代理过的getName方法共多少条指令

  public final java.lang.String getName(int) throws ;
    descriptor: (I)Ljava/lang/String;
    flags: ACC_PUBLIC, ACC_FINAL
    Code:
      stack=10, locals=3, args_size=2
         0: aload_0
         1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
         4: aload_0
         5: getstatic     #57                 // Field m3:Ljava/lang/reflect/Method;
         8: iconst_1
         9: anewarray     #22                 // class java/lang/Object
        12: dup
        13: iconst_0
        14: iload_1
        15: invokestatic  #63                 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
        18: aastore
        19: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;
        24: checkcast     #52                 // class java/lang/String
        27: areturn
        28: athrow
        29: astore_2
        30: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
        33: dup
        34: aload_2
        35: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
        38: athrow
      Exception table:
         from    to  target type
             0    28    28   Class java/lang/Error
             0    28    28   Class java/lang/RuntimeException
             0    28    29   Class java/lang/Throwable
    Exceptions:
      throws

如果不出错，到 27：areturn  至少要执行到13条指令 java8对动态代理有优化过

结论是:jdk动态代理比原生调用只慢几十毫秒，这点可以忽略不计