NIO problem: multiple write

Question

Hello.
I am using a NIO server for my application with a pool of WorkingThreads to handle client requests.
The read part seems to work fine (I am deregistering the OP_READ interest when I begin to read from the socketchannel and I register it back when I finish processing the data). This way I am able to process data coming in chunks down the stream.
Now, the problem I have is with writing data back to the client. If I send the data with only 1 socketChannel.write(ByteBuffer) method the client gets it correctly. But if I try to write in a while() loop more messages it happens that the client receives the first chunk correctly but SOMETIMES it receives rubbish as the next chunks. My guess is that after the first write(), the server may send some zeros to the client just before the next chunk so the client interprets that as valid data.
I have tried to unregister the key from writing (key.interestOps(key.interestOps() & (~SelectionKey.OP_WRITE))) immediatelly after I've done a write() and reregister it for writing just before I want to send the data but this didn't help. I'm sure this is solvable but I haven't met anywhere code that deals with writing more than 1 buffer (like writing a big file for example).
Any help would be very much appreciated.
Thank you.
Bogdan

Answer 1

Thank you for replying, ejp, but it seems that what you said is not quite true. Here is my send method:
public void send(SelectionKey key) {
     try {
          if (sendMessages.size() != 0) {
               String message = null;
               while (sendMessages.size() > 0) {
                    synchronized (sendMessages) {
                         message = (String) sendMessages.removeFirst();
                    ByteBuffer theBuffer = ByteBuffer.wrap(message.getBytes());
                    theBuffer.put(message.getBytes());
                    theBuffer.flip();
                    ((SocketChannel) key.channel()).write(theBuffer);
                    theBuffer.flip();
                    log.debug("Sent message:" + decoder.decode(theBuffer));
          key.interestOps(key.interestOps() | SelectionKey.OP_READ);
          key.interestOps(key.interestOps() & (~SelectionKey.OP_WRITE));
     } catch (IOException e) {
          key.cancel();
}I verify what I send by outputting with the line log.debug("Sent message:" + decoder.decode(theBuffer));The messages are strings which are being taken from a LinkedList. The chunks I'm sending are of size 4096 bytes.
I forgot to mention that the client uses simple IO (blocking mode). In between the sendings from the server it receives zeros and considers them as part of the message.
I am using Windows 2000 + JDK 1.4.2_01