Thread problem in JavaNIO client server application

Question

**Dear experts,**
I have problem with server which is nonblocking nio server, after registering one client the server is not registering other clients can some body told me, what is going on why sever is not showing any activity*
this is Tour proxy class which is at client site and dealing with server and updating GUI on client site:*
public void run() {
          connect(host);
          running = true;
          while (running) {
               readIncomingMessages();
               // nap for a bit
               try {
                    Thread.sleep(50);
               catch (InterruptedException ie) {
     } this is GUI which is dealing with Tourproxy
class WrapNetTour3D
void createSceneGraph(String userName, String tourFnm,
                                             double xPosn, double zPosn)
  // initialize the scene
    sceneBG = new BranchGroup();
    bounds = new BoundingSphere(new Point3d(0,0,0), BOUNDSIZE);
    // to allow clients to be added/removed from the world at run time
    sceneBG.setCapability(Group.ALLOW_CHILDREN_READ);
    sceneBG.setCapability(Group.ALLOW_CHILDREN_WRITE);
    sceneBG.setCapability(Group.ALLOW_CHILDREN_EXTEND);
    lightScene();         // add the lights
    addBackground();      // add the sky
    sceneBG.addChild( new CheckerFloor().getBG() );  // add the floor
    makeScenery(tourFnm);      // add scenery and obstacles
    TP = new TourProxy("localhost",this,obs);
    makeContact();     // contact server (after Obstacles object created)
    addTourist(userName, xPosn, zPosn);     
                            // add the user-controlled 3D sprite
    sceneBG.compile();   // fix the scene
  } // end of createSceneGraph()
private void makeContact()
  /* Contact the server, and set up a TourProxy to monitor the
     server. */
    try {
           TP.start();
    catch(Exception e)
    { System.out.println("No contact with server");
      System.exit(0);
  }  // end of makeContact()
....} this is class which is initializing the above class WrapNetTour3D:
  public NetTour3D(String args[])
    super("3D NetTour");
    processArgs(args);
    setTitle( getTitle() + " for " + userName);
    Container c = getContentPane();
    c.setLayout( new BorderLayout() );
    w3d = new WrapNetTour3D(userName, tourFnm, xPosn, zPosn);
    c.add(w3d, BorderLayout.CENTER);
     addWindowListener( new WindowAdapter() {
       public void windowClosing(WindowEvent e)
       { w3d.closeLink(); }
    pack();
    setResizable(false);    // fixed size display
    setVisible(true);
  } // end of NetTour3D() and this is server:
public NIOTourServer( String string, int port) throws IOException {
          this.addr = string;
          this.port = port;
          writeBuffer = ByteBuffer.allocateDirect(BUFFER_SIZE);
          dataMap = new HashMap<SocketChannel, List<byte[]>>();
          clients = new LinkedList();
          userName = "?";
          startServer();
     private void startServer() throws IOException {
          // create selector and channel
          this.selector = Selector.open();
          ServerSocketChannel serverChannel = ServerSocketChannel.open();
          serverChannel.configureBlocking(false);
          // bind to port
          InetSocketAddress listenAddr = new InetSocketAddress(this.addr,
                    this.port);
          serverChannel.socket().bind(listenAddr);
          serverChannel.register(this.selector, SelectionKey.OP_ACCEPT);
          log("Echo server ready. Ctrl-C to stop.");
          // processing
          while (true) {
               // wait for events
               this.selector.select();
               // wakeup to work on selected keys
               Iterator keys = this.selector.selectedKeys().iterator();
               while (keys.hasNext()) {
                    SelectionKey key = (SelectionKey) keys.next();
                    // this is necessary to prevent the same key from coming up
                    // again the next time around.
                    keys.remove();
                    if (!key.isValid()) {
                         continue;
                    if (key.isAcceptable()) {
                         this.accept(key);
                    } else if (key.isReadable()) {
                         this.read(key);
                    } else if (key.isWritable()) {
                         //this.write(key);
     private void accept(SelectionKey key) throws IOException {
          ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();
          SocketChannel channel = serverChannel.accept();
          clients.add(channel);
          log.info("got connection from: " + channel.socket().getInetAddress());
          channel.configureBlocking(false);
          // write welcome message
          channel.write(ByteBuffer.wrap("Welcome, this is the Tour server\r\n"
                    .getBytes("US-ASCII")));
          Socket socket = channel.socket();
          SocketAddress remoteAddr = socket.getRemoteSocketAddress();
          log.info("Connected to: " + remoteAddr);
          // register channel with selector for further IO
          dataMap.put(channel, new ArrayList<byte[]>());
          channel.register(this.selector, SelectionKey.OP_READ);
     private void sendMessage(SocketChannel channel, String mesg) {
          prepWriteBuffer(mesg);
          channelWrite(channel, writeBuffer);
     private void read(SelectionKey key) throws IOException {
          try {
               SocketChannel channel = (SocketChannel) key.channel();
               ByteBuffer buffer = ByteBuffer.allocate(4192);
               int numRead = -1;
               // read from the channel into our buffer
               numRead = channel.read(buffer);
               // check for end-of-stream
               if (numRead == -1) {
                    log.info("disconnect: " + channel.socket().getInetAddress()
                              + ", end-of-stream");
                    channel.close();
                    clients.remove(channel);
                    sendBroadcastMessage("logout: "
                              + channel.socket().getInetAddress(), channel);
               } else {
                    byte[] data = new byte[numRead];
                    System.arraycopy(buffer.array(), 0, data, 0, numRead);
                    String dataReturn = new String(data, "US-ASCII");
                    log("Got: " + dataReturn);
                    processClient(dataReturn,channel);
          } catch (IOException ioe) {
               log.warn("error during select(): ", ioe);
          } catch (Exception e) {
               log.error("exception in run()", e);
     private void processClient(String line,SocketChannel from)
     /* Stop when the input stream closes (is null) or "bye" is sent
           Otherwise pass the input to doRequest(). */
          //String line;
          boolean done = false;
          while (!done) {
               // if((line = in.readLine()) == null)
               if(line == null)
                    done = true;
               else {
                    // System.out.println(userName + " received msg: " + line);
                    if (line.trim().equals("bye"))
                         done = true;
                    else
                         doRequest(line.trim(), from);
     }  // end of processClient()
...} i thought there is some problem with threads
can somebody tell me how can i deal with it, as i m new newbie and how could i avoid problems in such design and complex application so that i am able to complete this application
please help,
thanks a lot
jibbylala
Edited by: 805185 on Nov 23, 2010 10:43 AM
Edited by: 805185 on Nov 23, 2010 11:36 AM

Answer 1

ejp:Here you are assuming that the socket is readable. Check it. You also need to check for isConnectable(), and if true, try finishConnect(), and if that succeeds deregister OP_CONNECT and register OP_READ.
where i do this or it should be  done in connect method() or in readIncomingMessages() .
the current problem is connecting 2nd client.
i thought the other steps came later
i changed the connect method like this :
private void connect(String hostname) {
          try {
               InetAddress addr = InetAddress.getByName(hostname);
               int mnInterestOps = 0;
               try
                    channel = SocketChannel.open();
                    channel.configureBlocking(false);
                    InetSocketAddress mxRemoteAddress = new InetSocketAddress(addr, PORT);
                    boolean t_connect = channel.connect(mxRemoteAddress);
                    if (t_connect)
                         System.out.println("connected");
                         mnInterestOps = SelectionKey.OP_WRITE | SelectionKey.OP_READ ;
                    else
                         mnInterestOps = SelectionKey.OP_CONNECT;
                    //create the selector
                    readSelector= SelectorProviderImpl.provider().openSelector();
                    //register the channel with the selector indicating an interest
                    SelectionKey x_key = channel.register(readSelector, mnInterestOps);
                    //select loop
                    while(true)
                         //block until connect response is received
                         int selectReturn = readSelector.select(0);
                         if (selectReturn == 0)
                              System.out.println("select returned 0");
                         Set myKeys = readSelector.selectedKeys();
                         if (!myKeys.isEmpty())
                              Iterator x_readyKeysIterator = myKeys.iterator();
                              // Iterate over the set of keys for which events are available
                              while (x_readyKeysIterator.hasNext())
                                   SelectionKey x_selectionKey = (SelectionKey) x_readyKeysIterator.next();
                                   // Remove selected key
                                   x_readyKeysIterator.remove();
                                   if (x_selectionKey.isValid())
                                        if (x_selectionKey.isConnectable()) {
                                             channel.finishConnect();
                                             System.out.println("connection 2 accepted");
                                        else if (x_selectionKey.isWritable()) {
                                             System.out.println("writable channel, select return =" + selectReturn);
                                             x_selectionKey.cancel();
                                        else if (x_selectionKey.isReadable()) {
                                             System.out.println("readable channel" + selectReturn);
                                   else
                                        //cancel the channel registration with this selector
                                        x_selectionKey.cancel();
                                        System.out.println("key not valid");
                    } //end while(true)
               } //end try block
               catch (Exception ex)
                    System.out.println("exception " + ex);
          catch (UnknownHostException uhe) {
               uhe.printStackTrace();
          catch (Exception e) {e.printStackTrace();
     } but now i m getting NPE HERE in tourproxy class.
this is method which is calling channelWrite() and this method sendMessage()  i m calling from different other gui classes and i don't think so that i need  to pass the channel from there:
void sendMessage(String mesg) {
          prepWriteBuffer(mesg);
          channelWrite(channel, writeBuffer);
private void channelWrite(SocketChannel channel, ByteBuffer writeBuffer) {
nbytes += channel.write(writeBuffer); *//channel is null here*
} *can you just  tell me why it is null as i m populating it in connect method or what should i do?
PS: i already created chat application with javaNIO....
The output of this application  is nothing but a sprite which has to move simultaneously on two clients but it is not because server can't register more than one client.