package com.test.server;
 
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
 
public class Server {
 
 public static void main(String[] args) {
 new Server().startServer();
 }
 
 public void startServer(){
 try {
  //服務器在9990端口監聽客戶端的連接
  ServerSocket ss = new ServerSocket(9999);
  System.out.println("server is listening...");
  while(true){
  //阻塞的accept方法，當一個客戶端連接上，才會返回Socket對象
  Socket s = ss.accept();
  System.out.println("a client has connected!");
  //開啟線程處理通信
  new CommunicateThread(s).start();
  }
 } catch (IOException e) {
  e.printStackTrace();
 }
 }
 
 public class CommunicateThread extends Thread{
 
 Socket socket;
 DataInputStream dis;
 DataOutputStream dos;
 
 public CommunicateThread(Socket socket){
  this.socket = socket;
  try {
  dis = new DataInputStream(socket.getInputStream());
  dos = new DataOutputStream(socket.getOutputStream());
  } catch (IOException e) {
  e.printStackTrace();
  }
 }
 
 @Override
 public void run() {
  super.run();
  //讀取客戶端發過來的消息
  String msg = null;
  try {
  while((msg = dis.readUTF()) != null){
   System.out.println("client send msg ：" + msg);
   String replyMsg = "server reply ： " + msg;
   dos.writeUTF(replyMsg);
   System.out.println("server reply msg ：" + replyMsg);
  }
  } catch (IOException e) {
  e.printStackTrace();
  }
 }
 }
 
}

package com.test.client;
 
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.util.Scanner;
 
public class Client {
 
 public static void main(String[] args) {
 new Client().startClient();
 }
 
 public void startClient(){
 try {
  //連接到服務器
  Socket socket = new Socket("localhost", 9999);
  DataInputStream dis = new DataInputStream(socket.getInputStream());
  DataOutputStream dos = new DataOutputStream(socket.getOutputStream());
  Scanner scanner = new Scanner(System.in);
  String line = null;
  listenServerReply(dis);
  while((line = scanner.nextLine()) != null){//讀取從鍵盤輸入的一行
  dos.writeUTF(line);//發給服務端
  System.out.println("client send msg : " + line);
  }
 } catch (Exception e) {
  e.printStackTrace();
 }
 }
 
 //監聽服務端回復的消息
 public void listenServerReply(final DataInputStream dis){
 new Thread(){
  @Override
  public void run() {
  super.run();
  String line = null;
  try {
   while((line = dis.readUTF()) != null){
   System.out.println("client receive msg from server: " + line);
   }
  } catch (IOException e) {
   e.printStackTrace();
  }
  }
 }.start();
 }
 
}