Java.nio.FileChannel tryLock() method does not lock!!!

Question

Hello,
I have the following:
           RandomAccessFile raf = new RandomAccessFile(file, "rw");
           try {
                 lock = raf.getChannel().tryLock();
          } catch (OverlappingFileLockException e) {
                  System.out.println("File is locked"); // this never gets printed
           if (lock != null) {
                  // successfully acquired a lock
                  System.out.println("acquired lock!!!"); // this gets printed alright
                  // check if lock is valid
                  System.out.println("is this lock valid?  "+lock.isValid()); // it always is when I run my app
                  // do stuff with the file
          ....Note that I do NOT close the channel, which would make the lock invalid.
Well, as far as I know, the code above tries to acquire an EXCLUSIVE lock (no read or write) on a file. It means that no other java application should be able to access that file, right?
My problem is that I can still open that file with a second instance of my app, regardless of the lock.
What am I missing?
PS: don't know if it's relevant, but I do this right AFTER acquiring the lock:
     InputStream stream = Channels.newInputStream(raf.getChannel());
     XMLDecoder d = new XMLDecoder(new BufferedInputStream(stream));                       

Answer 1

Thanks for the answer, mlk.
Well, I went through MSDN to find no answer. Anyway, now I noticed tryLock() blocks, and it shouldn't. I ran two instances of my app and the second one keeps waiting till I release the lock created on the first one!!! Here's some code:
            try
                lock = channel.tryLock();
                System.out.println("File not locked");
            catch (OverlappingFileLockException e)
                // File is already locked in this thread or virtual machine
                System.out.println("File locked");
             try
                BufferedReader in = new BufferedReader(new InputStreamReader(
                        System.in));
                String str = "";
                while (str != null)
                    System.out.print("> prompt ");
                    str = in.readLine();
                    if (str.equalsIgnoreCase("status")) {
                        System.out.println("lock = "+lock);
                    } else if (str.equalsIgnoreCase("exit")) break;
...As stated in the API docs, tryLock() should return immediately. Therefore, the 'lock = channel.tryLock();' should either return cleanly or throw an exception. Then, no matter what, 'prompt >' should appear in the console. Except it doesn't for the second instance. Exiting the first instance makes the second one print out 'prompt'. I believe this shows tryLock() was blocking the execution. Am I missing something?
Not being able to use file lock functionality has been annoying me for quite some time now. Urgh!!!!
Has someone used it on Windows with success? Is there another way of doing it (I know one could use native code, but I could not find example) ?
Thanks