PS: RPC远程调用  Webservice啥的都是远程调用。下面简单介绍其使用过程
    Hadoop已经实现了RPC框架，不用我们自己写，不过需要我们注意几点：
1.发布服务端和客户端必须包名相同

package cn.itcast.bigdata.hadooprpc.service;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.ipc.RPC;

import org.apache.hadoop.ipc.RPC.Builder;

import org.apache.hadoop.ipc.RPC.Server;

import cn.itcast.bigdata.hadooprpc.protocol.ClientNamenodeProtocol;

import cn.itcast.bigdata.hadooprpc.protocol.IUserLoginService;

public class PublishServiceUtil {

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

        Builder builder2 = new RPC.Builder(new Configuration());

        builder2.setBindAddress("localhost")

        .setPort(9999)

        .setProtocol(IUserLoginService.class)

        .setInstance(new UserLoginServiceImpl());

        Server server2 = builder2.build();

        server2.start();

    }

}

//服务与实现
package cn.itcast.bigdata.hadooprpc.protocol;

public interface IUserLoginService {

    public static final long versionID = 100L;

    public String login(String name,String passwd);

}

package cn.itcast.bigdata.hadooprpc.service;

import cn.itcast.bigdata.hadooprpc.protocol.IUserLoginService;

public class UserLoginServiceImpl implements IUserLoginService{

    @Override

    public String login(String name, String passwd) {

        return name + "logged in successfully...";

    }

}

package cn.itcast.bigdata.hadooprpc.client;

import java.io.IOException;

import java.net.InetSocketAddress;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.ipc.RPC;

import cn.itcast.bigdata.hadooprpc.protocol.IUserLoginService;

public class UserLoginActionStudy {

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

        IUserLoginService userLoginService = RPC.getProxy(IUserLoginService.class, 100L, new InetSocketAddress("localhost", 8888),new Configuration());

        String login = userLoginService.login("angelababy", "1314520");

        System.out.println(login);

    }

}