jdk动态代理的实现原理

jdk动态代理实际上是jvm帮我们建成的类实现我们传入的接口，加载字节码到jvm。实际上就是帮我们拼接的字符串和我们传进去的接口进行拼接，然后生成字节码加载进虚拟机。代理类持有InvocationHandler的引用，当我们调用方法时实际上调用的是InvocationHandler的引用的invoke方法，invoke方法中再进行反射调用方法。jdk动态代理只能代理接口

接口类：

public interface Person {
public void eat();
}

实现类：

public class Man implements Person{

    @Override
    public void eat() {
        System.out.print("我吃饭了");

    }

}

InvocationHandler的实现类：

public class MyHandler implements InvocationHandler{
    private Object object;
    public MyHandler(Object object) {

        this.object=object;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        // TODO Auto-generated method stub
                doBefore();
                Object result;
                result=method.invoke(this.object, args);//这里是不是很熟悉，可以看看反射
                doAfter();
                return result;
            }
        private void doBefore(){
            System.out.println("方法执行前");
        }
        private void doAfter(){
            System.out.println("方法执行后");
        }
        }

测试类：

public class Test {
public static void main(String[] args) {
    System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles","true");
    Person man=new Man();
    MyHandler handler=new MyHandler(man);
    Person proxy=(Person) Proxy.newProxyInstance(man.getClass().getClassLoader(), man.getClass().getInterfaces(), handler);
    System.out.println(proxy.getClass());
    proxy.eat();
}
}

System.getProperties().put(“sun.misc.ProxyGenerator.saveGeneratedFiles”,”true”);会保存生成的动态代理类$Proxy0，生成的代理类会自动新建文件夹存放在com/sun/proxy下

反编译后如下：

package com.sun.proxy;

import com.gjh.test.Person;
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 Person
{
  private static Method m1;
  private static Method m3;
  private static Method m2;
  private static Method m0;

  public $Proxy0(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 void eat()
    throws 
  {
    try
    {
      this.h.invoke(this, m3, null);
      return;
    }
    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 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") });
      m3 = Class.forName("com.gjh.test.Person").getMethod("eat", new Class[0]);
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      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());
  }
}