服务端：

package server;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;

public class TCPServer {

    private final int port;
    private ClientListener mListener;

    public TCPServer(int port){
        this.port = port;
    }

    public  boolean start(){
        try {
            ClientListener listener = new ClientListener(port);
            mListener = listener;
            listener.start();
        }catch (IOException e){
            e.printStackTrace();
            return false;
        }
        return true;
    }


    public  void stop(){
        if(mListener != null){
            mListener.exit();
        }
    }

    private static class ClientListener extends Thread{
        private ServerSocket server;
        private boolean done = false;

        private ClientListener(int port) throws IOException {
            server = new ServerSocket(port);
            System.out.println("服务器信息："+server.getInetAddress()+" P: "+port);
        }

        @Override
        public void run() {
            super.run();

            System.out.println("服务器准备就绪~");
            //等待客户端连接
            do{
                //得到客户端
                Socket client;
                try{
                    client = server.accept();
                }catch (IOException e){
                    continue;
                }
                //客户端构建异步线程
                ClientHandler clientHandler = new ClientHandler(client);
                //启动线程
                clientHandler.start();
            }while (!done);

            System.out.println("服务器已关闭! ");
        }

        void exit(){
            done = true;
            try{
                server.close();
            }catch (IOException e){
                e.printStackTrace();
            }
        }

        /**
         * 客户端消息处理
         */
        private static class ClientHandler extends Thread{
            private Socket socket;
            private boolean flag = true;

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

            @Override
            public void run() {
                super.run();
                System.out.println("新客户端连接: "+ socket.getInetAddress()+
                        " P:"+socket.getPort());
                try {
                    //得到打印流，用于数据输出；服务器回送数据使用
                    PrintStream socketOutput = new PrintStream(socket.getOutputStream());
                    //得到输入流，用于接收数据
                    BufferedReader socketInput = new BufferedReader(new InputStreamReader(socket.getInputStream()));

                    do{
                        //客户端拿到一条数据
                        String str = socketInput.readLine();
                        if("bye".equalsIgnoreCase(str)){
                            flag = false;
                            //回送
                            socketOutput.println("bye");
                        }else {
                            //打印到屏幕，并回送数据长度
                            System.out.println(str);
                            socketOutput.println("回送： "+ str.length());
                        }
                    }while (flag);
                    socketInput.close();
                    socketOutput.close();
                }catch (Exception e){

                }finally {
                    try {
                        socket.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println("客户端已退出：" + socket.getInetAddress() +
                        " P:" + socket.getPort());
            }
        }
    }
}

客户端：

package client;

import client.bean.ServerInfo;

import java.io.*;
import java.net.*;

public class TCPClient {
    public static void linkWith(ServerInfo info) throws IOException {
        Socket socket = new Socket();
        //超时时间
        socket.setSoTimeout(3000);
        //连接传输过来的地址，端口2000，超时时间3000ms
        socket.connect(new InetSocketAddress(Inet4Address.getByName(info.getAddress()),info.getPort()),3000);

        System.out.println("已发起服务器连接，并进入后续流程～");
        System.out.println("客户端信息：" + socket.getLocalAddress() + " P:" + socket.getLocalPort());
        System.out.println("服务器信息：" + socket.getInetAddress() + " P:" + socket.getPort());

        try{
            //发送接收数据
            todo(socket);
        }catch (Exception e){

        }finally {
            socket.close();
        }

        //释放资源
        socket.close();
        System.out.println("客户端已退出～");
    }

    private static void todo(Socket client) throws IOException {
        //构建键盘输入流
        InputStream in = System.in;
        BufferedReader input = new BufferedReader(new InputStreamReader(in));

        //得到Socket输出流，并转换为打印流
        OutputStream outputStream = client.getOutputStream();
        PrintStream socketPrintStream = new PrintStream(outputStream);

        //得到Socket输入流，并转换为BufferedReader
        InputStream inputStream = client.getInputStream();
        BufferedReader socketBufferedReader = new BufferedReader(new InputStreamReader(inputStream));

        boolean flag = true;
        do{
            //键盘读取一行
            String str = input.readLine();
            //发送到服务器
            socketPrintStream.println(str);

            //从服务器读取一行
            String echo = socketBufferedReader.readLine();
            if("bye".equalsIgnoreCase(echo)){
                flag = false;
            }else {
                System.out.println(echo);
            }
        }while (flag);

        //释放资源
        socketPrintStream.close();
        socketBufferedReader.close();
    }
}

运行结果：

客户端可以向服务端发送消息