要深入研究netty所以先写个BIO的服务端客户端之后做对比（可以多个客户端运行）

三个类

import java.io.*;
import java.net.Socket;
import java.util.Scanner;



public class Client {
    public static String IP = "127.0.0.1";
    public static int PORT = 12378;

    public static void main(String[] args) {
        try {
            Socket socket = new Socket(IP, PORT);

            System.out.println("请输出数据");
            new ReadMsg(socket).start();


            while (true) {
                PrintWriter writer = new PrintWriter(socket.getOutputStream());
                writer.println(new Scanner(System.in).next());
                writer.flush();

            }

        } catch (IOException e) {
            e.printStackTrace();
        }

    }


    private static class ReadMsg extends Thread {
        private Socket socket;

        ReadMsg(Socket socket) {
            this.socket = socket;
        }

        @Override
        public void run() {

            try {

                BufferedReader reader1 = new BufferedReader( new InputStreamReader(socket.getInputStream()));
                String line = null;
                while ((line = reader1.readLine()) != null) {
                    System.out.println(line);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            finally {
                clear();
            }

        }
        //必要的资源清理工作
        private void clear() {
            if (socket != null)
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
        }
    }
}

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Server {
    private static ServerSocket server;
    public static String IP = "127.0.0.1";
    public static int PORT = 12378;

    public  static  ExecutorService executorService = Executors.newFixedThreadPool(5);


    public static void start() throws IOException {

        try {

               server = new ServerSocket(PORT);
            while (true) {
                System.out.println("建立新连接");

                Socket socket = server.accept();
                executorService.execute(new ServerHandle(socket));
            }
            //Socket socket = server.accept();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally{
            if(server!=null){
                server.close();
            }
        }



    }

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

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class ServerHandle implements Runnable {
    private  Socket socket;
    ServerHandle (Socket socket)
    {
        this.socket=socket;
    }

    @Override
    public void run() {

        try {

            BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);
            String message;
            String result;
            while((message=reader.readLine()) !=null)
            {
                System.out.println("服务器收到数据："+message);
                writer.println(message);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally{
            if(socket != null){
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                socket = null;
            }
        }
    }

}

可以多开两个客户端测试。