A程序和B程序之间互发消息，其实AB程序每个都是两个线程的，一个线程用于监听（接收消息），一个程序用于访问端口（发送消息），详情参见代码，如果觉得对你有帮助，麻烦点个赞，欢迎讨论交流

项目地址：

Server

package com.changgx;/** * Created by Administrator on 2016/12/6. */import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.net.ServerSocket;import java.net.Socket;/** * 服务端 */public class Server extends Thread {    /**     * 监听端口     */    private int port;    public Server(int port) {        this.port=port;    }    @Override    public void run() {        try {            //设置监听端口            ServerSocket server = new ServerSocket(port);            //开始监听端口，没有连接，那么该方法会阻塞            Socket socket = server.accept();            //获取信息            BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));            String line = null;            while (!"quit".equalsIgnoreCase(line = br.readLine())) {                System.out.println("ta :" + line);            }            socket.close();            server.close();        } catch (IOException e) {            e.printStackTrace();        }    }    public static void main(String[] args) {        Thread server = new Server(10000);        Thread client = new Client("localhost",10001);        server.start();        client.start();    }}

Client

package com.changgx;/** * Created by Administrator on 2016/12/6. */import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.Socket;/** * 客户端 */public class Client extends Thread {    /**     * 请求的host地址     */    private String host;    /**     * 请求的端口     */    private int port;    public Client(String host, int port) {        this.host = host;        this.port = port;    }    @Override    public void run() {        try {            //获取键盘输入            BufferedReader input = new BufferedReader(new InputStreamReader(System.in));            //readline() 会一直等待键盘输入，只有输入后才会去创建socket连接            //如果先创建socket，会导致运行mian方法的时候，对方的server还没有启动，这边就去请求，会报错            //所以使用readline()来阻塞            String line = input.readLine();            //创建socket连接            Socket socket = new Socket(host, port);            PrintWriter pw = new PrintWriter(socket.getOutputStream());            //输入quit，退出客户端            while (!"quit".equalsIgnoreCase(line)) {                pw.println(line);                pw.flush();                line = input.readLine();            }            pw.println(line);            pw.close();            input.close();            socket.close();        } catch (IOException e) {            e.printStackTrace();        }    }    public static void main(String[] args) throws Exception {        Thread server = new Server(10001);        Thread client = new Client("localhost",10000);        server.start();        client.start();    }}