动态代理-JDK动态代理

引自：http://yy629.iteye.com/blog/681430
动态代理，可以对接口、类进行代理，其中jdk自带的动态代理，只能通过接口代理，其他如：asm、cglib、javaassist对两者均可代理，其中保存jdk动态类方法：

package demo;

import java.io.File;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Properties;

/**
 * @author yeyong
 */
public class ProxyTest2 {

  public static void main(String[] args) throws Exception {

    // 添加以下的几段代码, 就可以将代理生成的字节码保存起来了
    Field field = System.class.getDeclaredField("props");
    field.setAccessible(true);
    Properties props = (Properties) field.get(null);
    props.put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

    Package pkg = ProxyTest2.class.getPackage();
    if (pkg != null) {
      String packagePath = pkg.getName().replace(".", File.pathSeparator);
      new File(packagePath).mkdirs();
    }

    IA a = new IAImpl();
    InvocationHandlerImpl ih = new InvocationHandlerImpl(a);
    IA proxyA = (IA) Proxy.newProxyInstance(a.getClass().getClassLoader(),
         a.getClass().getInterfaces(), ih);

    proxyA.a();
  }
}

interface IA {
  void a();
  int b(String str);
}

class IAImpl implements IA {

  @Override
  public void a() {
    System.out.println("IAImpl.a()");
  }
  @Override
  public int b(String str) {
  System.out.println("IAImpl.b()");
    return 0;
  }
}

class InvocationHandlerImpl implements InvocationHandler {

  private Object target;

  public InvocationHandlerImpl(Object target) {
    this.target = target;
  }

  public Object invoke(Object proxy, Method method, Object[] args) 
      throws Throwable {
    System.out.println("before...");
    Object res = method.invoke(target, args);
    System.out.println("after...");
    return res;
  }
}

反编译后源码如下

package demo;

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

  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 (RuntimeException localRuntimeException) {
      throw localRuntimeException;
    } catch (Throwable localThrowable) {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final int b(String paramString) {
    try {
      return ((Integer) this.h.invoke(this, m4,
           new Object[] { paramString })).intValue();
    } catch (RuntimeException localRuntimeException) {
      throw localRuntimeException;
    } catch (Throwable localThrowable) {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final void a() {
    try {
      this.h.invoke(this, m3, null);
      return;
    } catch (RuntimeException localRuntimeException) {
      throw localRuntimeException;
    } catch (Throwable localThrowable) {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final int hashCode() {
    try {
      return ((Integer) this.h.invoke(this, m0, null)).intValue();
    } catch (RuntimeException localRuntimeException) {
      throw localRuntimeException;
    } catch (Throwable localThrowable) {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final String toString() {
    try {
      return (String) this.h.invoke(this, m2, null);
    } catch (RuntimeException localRuntimeException) {
      throw localRuntimeException;
    } catch (Throwable localThrowable) {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  static {
    try {
      m1 = Class.forName("java.lang.Object").getMethod("equals",
          new Class[] { Class.forName("java.lang.Object") });
      m4 = Class.forName("demo.IA").getMethod("b", 
          new Class[] { Class.forName("java.lang.String") });
      m3 = Class.forName("demo.IA").getMethod("a", new Class[0]);
      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
    } catch (NoSuchMethodException localNoSuchMethodException) {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    } catch (ClassNotFoundException localClassNotFoundException) {
      throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
    }
  }
}