Question

I have defined a class(callable) named “folderwatcher” that is monitoring a specific folder for any changes. The main code is in an infinite loop similar to: Monitor a Directory for Changes using Java. I want the method/class that calls this “folderwatcher” to listen for any events discovered by the “folderwatcher” and does some operations based on the event. Does anyone know how I can do this? Do I need an event handler? any examples?
thanks

Answer 1

First of all, it is wrong to use an infinite loop approach. if you are really using Callable then you are already using an ExecutorService. What you should use is a ScheduledExecutorService and schedule your code as a repeated task.

As far as an event handler, this is not hard to accomplish, for example:

interface FileDetectedHandler { void fileDetected(File f); }

public static void main(String[] args) {
  final ScheduledExecutorService scheduler = 
     Executors.newSingleThreadScheduledExecutor();
  final FileDetectedHandler h = new FileDetectedHandler(File f) {
    public void fileDetected(File f) {
      System.out.format("File detected: %s\n", f);
  }};
  final Runnable r = new Runnable() { public void run() {
    File f = null;
    //detect file
    if (f != null) h.fileDetected(f);
  }};
  scheduler.scheduleWithFixedDelay(r, 0, 2, TimeUnit.SECONDS);
}