查看JDK动态代理生成的类的内容

首先我们先定义一个接口：

public interface PersonInter {

    String test(String str);
}

public class JdkProxySourceClass {

	public static void writeClassToDisk(String path){

		byte[] classFile = ProxyGenerator.generateProxyClass("$proxy4", new Class[]{PersonInter.class});
		FileOutputStream fos = null;
		try {
			fos = new FileOutputStream(path);
			fos.write(classFile);
			fos.flush();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}finally{
			if(fos != null){
				try {
					fos.close();
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}

    @Test  
    public void testGenerateProxyClass() {  
    	JdkProxySourceClass.writeClassToDisk("D:/$Proxy4.class");  
    }  
}

OK接下来我们用反编译工具看一下生成的代理类源码：

import com.zkn.newlearn.gof.proxyhandler.PersonInter;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class Proxy4 extends Proxy
  implements PersonInter
{
  private static Method m1;
  private static Method m2;
  private static Method m3;
  private static Method m0;

  public Proxy4(InvocationHandler paramInvocationHandler)
    throws 
  {
    super(paramInvocationHandler);
  }

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

  public final String test(String paramString)
    throws 
  {
    try
    {
      return ((String)this.h.invoke(this, m3, new Object[] { paramString }));
    }
    catch (RuntimeException localRuntimeException)
    {
      throw localRuntimeException;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final int hashCode()
    throws 
  {
    try
    {
      return ((Integer)this.h.invoke(this, m0, null)).intValue();
    }
    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") });
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      m3 = Class.forName("com.zkn.newlearn.gof.proxyhandler.PersonInter").getMethod("test", new Class[] { Class.forName("java.lang.String") });
      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());
    }
  }
}

从反编译出来的源码中我们可以看到在静态代码块中得到了equals、toString、hashCode和PersonInter接口中test方法的Method对象。当我们调用PersonInter中的test方法的时候：

  public final String test(String paramString)
    throws 
  {
    try
    {
      return ((String)this.h.invoke(this, m3, new Object[] { paramString }));
    }
    catch (RuntimeException localRuntimeException)
    {
      throw localRuntimeException;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

其实是调用了InvocationHandler中的invoke方法，并传入了之前获取到的对应的Method和参数。在这里也简单的说一下为什么JDK的动态代理只能代理接口不能代理类，请注意看我们所得到的代理类的源码，注意看这一句：public final class Proxy4 extends Proxy implements PersonInter。生成的代理类默认继承了Proxy这个类，而java中又是单继承的，所以这里只能代理接口，不能代理类了。就像枚举类，不能继承别的枚举类一样。