聊天程序：客户端到客户端聊天

Question

Currently I'm working on this mini chat program in Java where multiple users should be able to log into the chat program and chat. Right now what my program does is log in users (Clients) to the Server, and what ever they say gets echoed back by the Server. What I want to do is be able to send a request to chat with another client directly.

My idea was to create a Hash map that holds the username of the client and its socket. When a client requests to chat with another client it looks for that user's username in the HashMap and if the other client agrees to chat then it connects the sockets. I'm not sure how to implement this and also my program only takes one input from the user and returns it from the Server and after that it stops I have no idea why. I've been trying to get this working for a while now, starting to give me headaches.

Here's the code:

Client Class:

package source;

import java.io.*;
import java.util.*;
import java.net.*;

public class Client implements Runnable {
    private Socket socket;
    private DataOutputStream dout;
    private DataInputStream din;
    // Constructor

    public Client() {
        // Code
    }

    public Client(String host, int port) {

        try {
            socket = new Socket(host, port);
            System.out.println("connected to " + socket);
            din = new DataInputStream(socket.getInputStream());
            dout = new DataOutputStream(socket.getOutputStream());
            new Thread(this).start();
        } catch (IOException ie) {
            System.out.println(ie);
        }
    }

    private void processMessage(String message) {
        try {
            dout.writeUTF(message);
        } catch (IOException ie) {
            System.out.println(ie);
        }
    }

    public void run() {
        try {
            while (true) {
                String message = din.readUTF();
                System.out.println(message);
            }
        } catch (IOException ie) {
            System.out.println(ie);
        }
    }

    public static void main(String[] args) throws IOException {
        while (true) {
            String prompt;
            Scanner clientPrompt = new Scanner(System.in);
            System.out.println("client> ");
            prompt = clientPrompt.next();
            if (prompt.equals("Emmanuel"))
                System.out.println("God With Us");
            else if (prompt.equals("goOnline")) {
                // Enter a host name
                // Enter a portNumber
                // Enter a userName
                String h, p, u;
                System.out.println("Enter hostname: ");
                h = clientPrompt.next();
                System.out.println("Enter portNumber: ");
                p = clientPrompt.next();
                System.out.println("Enter userName: ");
                u = clientPrompt.next();
                goOnline(h, p, u);
            } else if (prompt.equals("Exit")) {
                clientPrompt.close();
                System.exit(1);
            } else {
                System.out.println("Invalid Input, Try Again");
            }
        }
    }

    public static void goOnline(String host, String port, String userName) {
        int portNumber = Integer.parseInt(port);
        Client c = new Client(host, portNumber);
        c.processMessage("Username: " + userName);
        String prompt;
        Scanner clientPrompt = new Scanner(System.in);
        while (true) {

            prompt = clientPrompt.next();
            c.processMessage(prompt);
            c.run();
            if (prompt.equals("Exit")) {
                System.out.println("Bye Bye");
                clientPrompt.close();
            }
        }
    }
}

Server Class:

package source;

import java.io.*;
import java.net.*;
import java.util.*;

public class Server { // The ServerSocket we'll use for accepting new
                        // connections
    private ServerSocket ss;

    private HashMap<String, Socket> userInfo = new HashMap<String, Socket>();

    // A mapping from sockets to DataOutputStreams.
    private Hashtable<Socket, DataOutputStream> outputStreams = new Hashtable<Socket, DataOutputStream>();

    // Constructor and while-accept loop all in one.
    public Server(int port) throws IOException {
        // All we have to do is listen
        listen(port);
    }

    private void listen(int port) throws IOException {
        // ServerSocket
        ss = new ServerSocket(port);
        System.out.println("Listening on " + ss);
        while (true) {
            Socket s = ss.accept();
            System.out.println("Connection from " + s);
            DataOutputStream dout = new DataOutputStream(s.getOutputStream());
            DataOutputStream userInfo = new DataOutputStream(s.getOutputStream());
            outputStreams.put(s, dout);
            outputStreams.put(s, userInfo);
            new ServerThread(this, s);
        }
    }

    Enumeration<DataOutputStream> getOutputStreams() {
        return outputStreams.elements();
    }

    void sendToAll(String message) {
        for (Enumeration<DataOutputStream> e = getOutputStreams(); e.hasMoreElements();) {
            // Output Stream
            DataOutputStream dout = (DataOutputStream) e.nextElement();
            // Send Message
            try {
                dout.writeUTF(message);
            } catch (IOException ie) {
                System.out.println(ie);
            }
        }
    }

    // Remove socket,
    void removeConnection(Socket s) {
        // Synchronize
        synchronized (outputStreams) {
            // Tell the world
            System.out.println("Removing connection to " + s);
            // Remove it from hashtable
            outputStreams.remove(s);
            try {
                s.close();
            } catch (IOException ie) {
                System.out.println("Error closing " + s);
                ie.printStackTrace();
            }
        }
    }

    void addInfo(String user, Socket s) {
        userInfo.put(user, s);
    }

    // Main
    static public void main(String args[]) throws Exception {
        // Get port
        int port = Integer.parseInt(args[0]);
        // Create Server object
        new Server(port);
    }
}

ServerThread:

package source;

import java.io.*;
import java.util.*;
import java.net.*;

public class ServerThread extends Thread { // The Server that spawned us
    private Server server;
    private Socket socket;

    public ServerThread(Server server, Socket socket) {
        this.server = server;
        this.socket = socket;
        start();
    }

    public void run() {
        try {
            DataInputStream din = new DataInputStream(socket.getInputStream());
            while (true) {
                String message = din.readUTF();
                StringTokenizer stt = new StringTokenizer(message, " ");
                while (stt.hasMoreTokens()) {
                    String token = stt.nextToken();
                    if (token.equals("Username:")) {
                        String username = stt.nextToken();
                        server.addInfo(username, socket);
                    }
                }
                System.out.println("Sending " + message);

                server.sendToAll(message);
                if (message.equals("Exit")) {
                    System.out.println("Bye Bye");
                    server.removeConnection(socket);
                    System.exit(1);
                }
            }
        } catch (EOFException ie) {
        } catch (IOException ie) {
            ie.printStackTrace();
        } finally {
            server.removeConnection(socket);
        }
    }
}

Answer 1

my program only takes one input from the user and returns it from the Server and after that it stops I have no idea why?

Just do one change as mentioned below at client side to resolve above issue.

public void run() {
    try {
        // while (true) { // remove an infinite loop that will block 
                          // the client thread to accept next message
        String message = din.readUTF();
        System.out.println(message);
        // }
    } catch (IOException ie) {
        System.out.println(ie);
    }
}

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Doubt: (client side)

• You have started a thread then why are you calling run() method directly.