jdk动态代理实现原理

jdk动态代理实现例子

一 接口

public interface CountService {
	int count();
}

二 具体实现类

public class CountServiceImpl implements CountService {

	private int count = 0;

	public int count() {
		
	System.out.println("count= " + count); 	
	return count ++;
	}

}

三 jdk处理类

	//jdk处理类
	private static class JdkHandler implements InvocationHandler {

	final Object delegate;

	JdkHandler(Object delegate) {
	this.delegate = delegate;
	}

	public Object invoke(Object object, Method method, Object[] objects)
	throws Throwable
	{
	 //System.out.println(" JDK Proxy invoke "+method.getName());	
	 return method.invoke(delegate, objects);
	}
	}

四 具体使用代码

public class DynamicProxyPerformanceTest {

	public static void main(String[] args) throws Exception {
		
		
		CountService delegate = new CountServiceImpl();

		
		long time = System.currentTimeMillis();
		
		
		CountService jdkProxy = createJdkDynamicProxy(delegate);
		time = System.currentTimeMillis()- time;
		System.out.println("Create JDK Proxy: " + time + " ms");
		
		jdkProxy.count();
		
	     byte[] bt=ProxyGenerator.generateProxyClass("Jdk$Proxy", CountServiceImpl.class.getInterfaces());
			
			
			OutputStream outs=new FileOutputStream(new File("E:/Jdk$Proxy.class"));
			outs.write(bt);
			outs.flush();
			outs.close();
	

		
		
		}

}

这样我们就实现了简单的jdk动态代理,那jdk动态代理类具体是怎么生成的呢？jdk动态代理类又是怎么调用jdk处理类的invoke方法的呢？

没办法只能查看源代码了

 public static Class<?> getProxyClass(ClassLoader loader,
                                         Class<?>... interfaces)
        throws IllegalArgumentException
    {


 /*
                 * Generate the specified proxy class.
                 */
                byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                    proxyName, interfaces);
                try {
                    proxyClass = defineClass0(loader, proxyName,
                        proxyClassFile, 0, proxyClassFile.length);
                } catch (ClassFormatError e) {
                    /*
                     * A ClassFormatError here means that (barring bugs in the
                     * proxy class generation code) there was some other
                     * invalid aspect of the arguments supplied to the proxy
                     * class creation (such as virtual machine limitations
                     * exceeded).
                     */
                    throw new IllegalArgumentException(e.toString());
                }

}

从上可见是通过ProxyGenerator类的generateProxyClass方法产生动态代理类的字节流

那jdk动态代理类又是怎么调用jdk处理类的invoke方法的呢？看来我们要是能生成具体jdk动态代理类的字节码就好了？既然ProxyGenerator类的generateProxyClass方法能产生动态类的字节流，我们把字节流保存到文件，再通过反编译工具就能看到具体的jdk动态代理类的源代码了。

通过反编译工具得到的动态代理类源代码如下

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
import test.kkfun.funbox.test.proxy.CountService;

public final class Jdk$Proxy extends Proxy
  implements CountService
{
  private static Method m1;
  private static Method m3;
  private static Method m0;
  private static Method m2;

  public Jdk$Proxy(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 int count()
    throws 
  {
    try
    {
      return ((Integer)this.h.invoke(this, m3, null)).intValue();
    }
    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);
  }

  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);
  }

  static
  {
    try
    {
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m3 = Class.forName("test.kkfun.funbox.test.proxy.CountService").getMethod("count", 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]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
    }
    throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
  }
}

通过查看JDK动态代理类的源代码的count方法

return ((Integer)this.h.invoke(this, m3, null)).intValue();

可见在动态代理类是直接调用注入的InvocationHandler对象的invoke方法来实现代理的