多客户端Java客户端服务器聊天

Question

I'm tryinna write a multiple client server chat. Everything should run on the same computer, each client in the different shell terminal console. I read couple of threads on this side, where people said, that I should run new thread on server for every single connected client. So that's what I've done.Still,Server is printing messages from every client on its console but clients can see only messages they wrote, not every message submitted on chat. What should I do to fix it?

Here is code: Server:

//package javauj.serwer;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;


public class Server {
    private static final int PORT_NUM = 5051;
    private static ServerSocket serS;
    private static Socket s;

    public static void main(String[] args) throws IOException{
        DateFormat df = new SimpleDateFormat("dd/MM/yy HH:mm:ss");
        Calendar cal = Calendar.getInstance();
            System.out.println(df.format(cal.getTime())+" Server waiting on port "+PORT_NUM);
            try {
                serS = new ServerSocket(PORT_NUM);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }



        while(true){
            try {
                s = serS.accept();
                System.out.println("New user connected");
                    ServerThread st=new ServerThread(s);
                        st.start();


                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }   





        }
    }
}   

Server Thread:

import java.io.IOException;
import java.io.PrintStream;
import java.net.Socket;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Scanner;


public class ServerThread extends Thread {
    Socket socket=null;
    private Scanner sc;
    private PrintStream ps;
    public ServerThread(Socket s) {
        this.socket=s;

    }



        public void run(){
            DateFormat df = new SimpleDateFormat("dd/MM/yy HH:mm:ss");
            Calendar cal = Calendar.getInstance();
            String response;    
                while(true){    
                try {
                        sc = new Scanner(socket.getInputStream());
                        ps = new PrintStream(socket.getOutputStream());
                } catch (IOException e) {
                            // TODO Auto-generated catch block
                        e.printStackTrace();
                }

                if((response=sc.nextLine())!=null){


                    System.out.println(df.format(cal.getTime())+" Napisal "+response);

                    ps.println(df.format(cal.getTime())+" Napisal :"+response);

                    }   
            }


        }


}

and Client

import java.io.IOException;
import java.io.PrintStream;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;




public class Client {
    static Scanner sc;
    static Scanner sc2;
    static Socket s;
    static String response;
    public static void main(String[]args) throws UnknownHostException, IOException{
        String send;
        sc=new Scanner(System.in);  //client send scanner
        s = new Socket("127.0.0.1", 5051);
        sc2 = new Scanner(s.getInputStream());  //client response scanner
        PrintStream ps = new PrintStream(s.getOutputStream());

        while(true){

            System.out.println(">");    
            send = sc.nextLine();

            ps.println(send);       
            // I tried run new thread for responses
            //Thread thread = new Thread(new Runnable(){
                //public void run(){
                    //while(true){
                        response=sc2.nextLine();        
                        System.out.println(response);
                //  }   
                //}
            //});
        }

    }
}

Answer 1

You need two threads on the client side:

• one to read messages coming from the server
• another thread to get the input from the user

The first thread (reader from server) simply reads incoming messages and print it to the console

The second thread (writer to the server) take user input and send it to the server.

Actually in your code there is only one thread on the client (the main thread).

Answer 2

1. You have to implement the communication (by an interface for example) between the instance of your ServerThread and the Server. The Server have to be notified about the message acquired by the ServerThread and then translate this message to the other (previously established) Sockets (which are must be tracked).

2. Your client have two Scanners, but one of them actually blocks the other on nextLine() call. So you have to run one of the Scanners in separate thread.

The following code works for me but the thread safety must be taken into account:

public interface MessageListener {
  void acceptMessage(String message);
}

public class Server {
  private static final int PORT_NUM = 5051;
  private static ServerSocket serS;
  private static List<PrintStream> sockets = new ArrayList<PrintStream>();
  public static void main(String[] args) throws IOException{
    DateFormat df = new SimpleDateFormat("dd/MM/yy HH:mm:ss");
    Calendar cal = Calendar.getInstance();
    System.out.println(df.format(cal.getTime())+" Server waiting on port "+PORT_NUM);
    try {
        serS = new ServerSocket(PORT_NUM);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    MessageListener listener = new MessageListener() {
        @Override
        public void acceptMessage(String message) {
            Iterator<PrintStream> it = sockets.iterator();
            while (it.hasNext()) {
                PrintStream ps = it.next();
                ps.println("Have got message: " + message);
            }
        }
    };

    while(true){
        try {
            Socket s = serS.accept();
            sockets.add(new PrintStream(s.getOutputStream()));
            System.out.println("New user connected");
            ServerThread st=new ServerThread(s, listener);
            st.start();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }



    }
}


public class ServerThread extends Thread {
  Socket socket=null;
  private Scanner sc;
  //private PrintStream ps;
  private final MessageListener listener;

  public ServerThread(Socket s, MessageListener listener) {
    this.socket=s;
    this.listener = listener;
  }

  public void run(){
    DateFormat df = new SimpleDateFormat("dd/MM/yy HH:mm:ss");
    Calendar cal = Calendar.getInstance();
    String response;
    while(true){
        try {
            sc = new Scanner(socket.getInputStream());
            //ps = new PrintStream(socket.getOutputStream());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        if((response=sc.nextLine())!=null){


            System.out.println(df.format(cal.getTime())+" Napisal "+response);

            //ps.println(df.format(cal.getTime())+" Napisal :"+response);
            listener.acceptMessage(response);
        }
      }


  }


}

public class Client {
  static Scanner sc;
  static Scanner sc2;
  static Socket s;
  static String response;
  public static void main(String[]args) throws UnknownHostException, IOException{
    String send;
    sc=new Scanner(System.in);  //client send scanner
    s = new Socket("127.0.0.1", 5051);
    ResponseListener l = new ResponseListener(new Scanner(s.getInputStream()));
    Thread t = new Thread(l);
    t.start();

    PrintStream ps = new PrintStream(s.getOutputStream());

    while(true){

        System.out.println(">");
        send = sc.nextLine();

        ps.println(send);
    }

}

static class ResponseListener implements Runnable {
    private final Scanner scanner;

    ResponseListener(Scanner scanner) {
        this.scanner = scanner;
    }

    @Override
    public void run() {
        while (true) {
            response = scanner.nextLine();
            System.out.println(response);
        }
    }
}

}