Question

Hello everyone i have created a multi threaded chat server that looks like this:

    public class Main {

    public static ServerSocket server;
    public static Socket connection;
    public static int backLog = 100;
    public static int numberOfConnected;
    public static boolean connected = false;
    public final static int potNumber = 6080;
    public static PrintWriter pw;
    public static Scanner input;
    public static int i = 0;

    public static void main(String[] args) {
        startServer();

    }
    public static void startServer(){
        try {
            server = new ServerSocket(potNumber, backLog);
            waitingForConnection();

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    private static void waitingForConnection() {
        connected = false;
        i++;
        while (!connected) {
            try {
                if (connected) {

                }
                connection = server.accept();
                Server s = new Server(connection, pw = new PrintWriter(connection.getOutputStream()), input = new Scanner(connection.getInputStream()));
                s.start();
                numberOfConnected++;
                waitingForConnection();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

}

The idea is that this is suppose to be a chat server so when one connects to the server it starts the following thread:

threads

    public void run(){
    while (connection.isConnected()) {
        if (input.hasNext()) {
            String fullMessage = input.nextLine();
            if (fullMessage.equalsIgnoreCase("Connect")) {
                connectHim();
            }else {
                chatMessage(fullMessage);
            }
        }

        }
    }

private void chatMessage(String fullMessage) {
    String name = fullMessage.substring(0, fullMessage.indexOf(" "));
    String message = fullMessage.substring(fullMessage.indexOf(" "), fullMessage.length());
    pw.println(name+": "+message);
    pw.flush();

}
private void connectHim() {
    String name = input.nextLine();
    pw.println(0);
    pw.flush();
    pw.println(1);
    pw.flush();
    pw.println();
    pw.flush();
    pw.println(name);
    pw.flush();

}

So my problem is the following:

if the user that is bound to thread 1 (this is an example) and the user bound to thread 2 sends a message to the server how will i send that message to the user bound on thread 1?

Answer 1

One of options is to use Hashtable or HashMap (just call Collections.synchronizedMap(myMap) in case of Map usage). When you start new Thread, give him unique name (for example user nick name ) and put it to your collection where key – Thread name, and value – Thread as Object.

if the user that is bound to thread 1 (this is an example) and the user bound to thread 2 sends a message to the server how will i send that message to the user bound on thread 1?

For example you have user1, user2, user3. Now you build 3 Threads and put them to HashMap, like:

Map<String, Thread> threadMap = new HashMap<String,Thread>();
    threadMap = Collections.synchronizedMap(threadMap);



    YourThread th1 = new YourThread();
            threadMap.put("user1", th);

    YourThread th2 = new YourThread();
            threadMap.put("user2", th);

    YourThread th3 = new YourThread();
            threadMap.put("user3", th);

             ....

    Set<String> userSet = threadMap.keySet();

    Iterator<String> it = userSet.iterator();

    Thread currThread = null;

    while(it.hasNext()){
        String key = it.next();

        currThread = threadMap.get(key);

        // do something with currThread         
    }