server服务端（使用线程池，减少线程创建销毁的消耗）

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

public class TcpEchoThreadServer {
    private ServerSocket serverSocket = null;

    public TcpEchoThreadServer(int port) throws IOException {
        serverSocket = new ServerSocket(port);
    }

    public void start() throws IOException {
        System.out.println("服务器启动");

        //先创建一个线程池实例
        ExecutorService executorService = Executors.newCachedThreadPool();

        while(true){
            //针对这个连接，单独创建一个线程负责处理
            Socket clientSocket = serverSocket.accept();
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    processConnection(clientSocket);
                }
            });
        }
    }
    public void processConnection(Socket clientSocket){
        System.out.printf("[%s:%d] 客户端上线!\n",clientSocket.getInetAddress().toString(),clientSocket.getPort());
        try(BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(clientSocket.getOutputStream()))){
             while(true){
                 //1.读取请求并解析
                 String request = bufferedReader.readLine();
                 //2.根据请求计算响应
                 String response = process(request);
                 //3.把响应写回到客户端
                 bufferedWriter.write(response+"\n");
                 bufferedWriter.flush();

                 System.out.printf("[%s:%d] rep: %s;resp: %s\n",clientSocket.getInetAddress().toString(),
                         clientSocket.getPort(),request,response);
             }
        }catch(IOException e){
            //e.printStackTrace();
            System.out.printf("[%s:%d] 客户端下线!\n",clientSocket.getInetAddress().toString(),clientSocket.getPort());
        }
    }

    private String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        TcpEchoThreadServer server = new TcpEchoThreadServer(9090);
        server.start();
    }
}

client服务端：
1.启动客户端（不绑定端口号）和服务器建立连接
2.进入主循环
a)读取用户输入内容
b)构造一个请求发送给服务器
c)读取服务器的响应数据
d)把响应数据显示到界面上

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

public class TcpEchoClient {
    private Socket socket = null;

    public TcpEchoClient(String serverIp,int serverPort) throws IOException {
        //此处的实例化Socket过程，就是在建立TCP连接
        socket = new Socket(serverIp,serverPort);
    }

    public void start() {
        System.out.println("客户端启动");
        Scanner scanner = new Scanner(System.in);
        try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
             BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()))) {
            while (true) {
                //读取用户输入内容
                System.out.println("->");
                String request = scanner.nextLine();
                if ("exit".equals(request)) {
                    break;
                }
                //构造请求并发送给服务器，此处用 \n 是为了和服务器中的readLine相对应
                bufferedWriter.write(request + "\n");
                bufferedWriter.flush();
                //读取服务器的响应数据
                String response = bufferedReader.readLine();
                //把响应数据显示到界面上
                System.out.println(response);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws IOException {
        TcpEchoClient client = new TcpEchoClient("127.0.0.1",9090);
        client.start();
    }
}