If you ask about file locks, the following example from the Depot example shows how to use it:
try { // Get a file channel for the file File file = new File("filename"); FileChannel channel = new RandomAccessFile(file, "rw").getChannel(); // Use the file channel to create a lock on the file. // This method blocks until it can retrieve the lock. FileLock lock = channel.lock(); // Try acquiring the lock without blocking. This method returns // null or throws an exception if the file is already locked. try { lock = channel.tryLock(); } catch (OverlappingFileLockException e) { // File is already locked in this thread or virtual machine } // Release the lock lock.release(); // Close the file channel.close(); } catch (Exception e) { }