JDK动态代理

RPC框架中，我们直接调用别人提供的接口，就执行InnovationHandler中invoke方法实现方法的远程调用逻辑。这是大家所熟知的，但是InnovationHandler的invoke方法被谁调用？什么时候调用？接下来我们用jdk动态代理来一探究竟：
接口：

interface IUser {
    public String sayHello(String hello) ;
}

实现：

class UserImpl implements IUser{

    @Override
    public String sayHello(String hello) {
        System.out.println(hello);
        return hello;
    }
}

测试类

class TestProxy{
    public static void main(String[] args) {
        //让jvm生成的代理类保存到本地       
        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
        System.out.println(Proxy.getProxyClass(IUser.class.getClassLoader(), IUser.class));

        UserImpl user = new UserImpl();
        IUser userProxy = (IUser)Proxy.newProxyInstance(user.getClass().getClassLoader(), user.getClass().getInterfaces(), new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                System.out.println("代理类开始工作");
                //如果是RPC框架，这里会启动序列化方案，以及通信调用数据；
                return method.invoke(proxy, args);
            }
        });
        userProxy.sayHello("hello");
    }
}

生成代理对象：

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 IUser {
    private static Method m1;
    private static Method m3;
    private static Method m0;
    private static Method m2;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return ((Boolean)super.h.invoke(this, m1, new Object[]{var1})).booleanValue();
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String sayHello(String var1) throws  {
        try {
            return (String)super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final int hashCode() throws  {
        try {
            return ((Integer)super.h.invoke(this, m0, (Object[])null)).intValue();
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m3 = Class.forName("com.jd.pops.settlement.manager.impl.IUser").getMethod("sayHello", Class.forName("java.lang.String"));
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
            m2 = Class.forName("java.lang.Object").getMethod("toString");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

真相大白：可以看到生成代理类中sayHello方法如下：

public final String sayHello(String var1) throws  {
        try {
            return (String)super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

至此，我们找到是代理类自己调用了成员invocationHandler的invoke方法，从而实现了方法的调用。