可以实现互相监听、互发消息，需要先运行服务器端，在运行客户端！

服务器端实现代码：

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


public class Server {
    public static void main(String[] args) {
        try {
            ServerSocket ss = new ServerSocket(8888);
            System.out.println("服务器已启动");
            Socket s = ss.accept();
            Scanner in = new Scanner(System.in);
            String temp;
            //构建IO流
            while(true){
                BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
                String mess = br.readLine();
                System.out.println("客户端>> "+mess);
                BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
                System.out.println("请输入发送消息内容：");
                temp=in.next();
                String str = temp+"\n";
                bw.write(str);
                bw.flush();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客户端实现代码：

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

public class Client {
    public static void main(String[] args) {
        try {
            Socket s = new Socket("127.0.0.1",8888);
            System.out.println("客户端IP:"+s.getLocalAddress()+"  端口"+s.getPort());
            BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
            Scanner scanner = new Scanner(System.in);
            while(true){
                System.out.println("请输入发送消息内容：");
                String temp=scanner.next();
                bw.write(temp+"\n");
                bw.newLine();
                bw.flush();
                BufferedReader br = new BufferedReader(new InputStreamReader(s.getInputStream()));
                System.out.println("服务器>> "+br.readLine());
            }
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行截图：