The Chat Application

Data members

  HashMap clientSockets = new HashMap();
  ServerSocket serverSocket;

The Constructor

  public ChatServer(int port) throws IOException {
    serverSocket = new ServerSocket(port);
  }

While-Accept loop

 protected void clientConnectListener() throws IOException {
    while (true) {
      Socket newSocket = serverSocket.accept();
      clientSockets.put(newSocket, 
        new DataOutputStream(newSocket.getOutputStream()));
      new ServerThread(this, newSocket);  // an independ thread for each client
    }
 }

The sendToAll(String message) method

  synchronized protected void sendToAll(String message) {
    Iterator it = clientSockets.values().iterator();
    while (it.hasNext()) {
      DataOutputStream dout = (DataOutputStream)it.next();
      try {
        dout.writeUTF(message);
      } catch (IOException e) {
        System.out.println("Error writing to client: " + e);
      }
    }
  }

The removeConnection(Socket socket) method.

 synchronized protected void removeConnection(Socket socket) {
   clientSockets.remove(socket);
 }

The main() method

  int port = Integer.parseInt(args[0]);
  ...
  new ChatServer(port).clientConnectListener();

The run() method should implements a while loop that read message from the client and passes the message to the server.

 protected ServerThread(ChatServer server, Socket socket) {
   this.server = server;
   this.socket = socket;
   start();
 } 
 public void run() {
   while(true) {
     ...  // read message from client
     server.sendToAll(message);
     ...  // if EOFException occurs inform the server to remove
          // this client socket from the list of client of socket,
          // and terminate the thread/method
   }
 }

The Constructor

  public ChatClient(String host, int port) throws IOException {
    ... // Establish connection to the server
    ... // Build the GUI
    new Thread(this).start(); // start the server message loop
  }

The user interface - consists of a JTextArea for displaying messages sent from the ChatServer, and a JTextFiled for user to input their messages.

User Input handling - an ActionListener to handler ActionPerformed Event of a JTextField and send the content to the ChatServer

A thread to read the message from the ChatServer and append to a JTextArea

  public void run() {
     try {
       while (true) {
         ... // read message from ChatServer
         textArea.append(message + "\n");
       }
     } catch (...) {
       ...
     }
  }

The main() method

  public static void main(String args[]) {
    ChatClient client = null;
    try {
      client = new ChatClient(args[0], Integer.parseInt(args[1]));
    } catch (IOException e) {
      System.out.println("Unable to establish connection to server" + e);
      System.exit(0);
    }
    client.pack();
    client.setVisible(true);
  }