JAVA实现简陋聊天室为什么输出两次输入一次?

Question

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;

/**

• 聊天室客户端

• @author Administrator
  *
  */
  public class Client {

  private Socket socket;
  /**

  • 构造方法,用来初始化客户端
    */
    public Client() {
    try {

    System.out.println("正在连接服务端........");
    socket =new Socket("localhost",8088);
    System.out.println("已连接服务端");
    

    } catch (UnknownHostException e) {
    e.printStackTrace();
    } catch (IOException e) {
    e.printStackTrace();
    }
    }
    /**

  • 客户端开始工作的方法
    */
    public void start() {

    try {
    OutputStream out=socket.getOutputStream();
    OutputStreamWriter osw=new OutputStreamWriter(out,"UTF-8");
    BufferedWriter bw=new BufferedWriter(osw);
    PrintWriter pw=new PrintWriter(bw,true);
    Scanner scan=new Scanner(System.in);
    String line;
    System.out.println("输入exit即可退出服务器");

    while(true) {
        line=scan.nextLine();
        if("exit".equals(line.toLowerCase())) {
            pw.println("exit");
            break;
        }
        pw.flush();
        pw.println(line);
    }
    pw.close();
    

    }catch(Exception e) {
    e.printStackTrace();
    }
    }
    public static void main(String[] args) {
    Client client=new Client();
    client.start();
    }
    }

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

/**

• 聊天室服务端

• @author Administrator
  *
  */
  public class Server {

  private ServerSocket server;
  /**

  • 构造方法,用来初始化服务端 */ public Server() { try { System.out.println("正在启动客户端......"); server=new ServerSocket(8088); System.out.println("客户端启动完毕 !"); } catch (IOException e) { e.printStackTrace(); }

  }
  /**

  • 服务端开始工作的方法
    
    */
    public void start() {
    try {

    System.out.println("等待客户端连接......");
    Socket socket=server.accept();
    System.out.println("一个客户端连接了");
    InputStream in=socket.getInputStream();
    InputStreamReader isr=new InputStreamReader(in,"UTF-8");
    BufferedReader br=new BufferedReader(isr);  
    while(true) {
        if("exit".equals(br.readLine())) {
            System.out.println("客户端已退出");
    
            break;
        }
        System.out.println(br.readLine());
    }
    br.close();
    

    } catch (IOException e) {
    e.printStackTrace();
    }
    }

  public static void main(String[] args) {
  Server server=new Server();
  server.start();
  }

}

Answer 1

readline是读取一行，你在判断和打印的时候都操作了readline，所以第二次才打印出来。server修改为

                String s = br.readLine();
                if ("exit".equals(s)) {
                    System.out.println("客户端已退出");
                    break;
                }
                System.out.println(s);