How can i stop WatchService (java)

Question

How can I stop the execution:

key = watchService.take()

my code:

//Watcher
public class DirectoryWatcherExample {

    public static void main(String[] args) throws IOException, InterruptedException {

        WatchService watchService = FileSystems.getDefault().newWatchService();
        //My folder
        Path path = Paths.get("D:\\java\\Input");
        
        path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);
        WatchKey key;
        while (((key = watchService.take()) != null)) {
            
            System.out.println(key);
            System.out.println(key.toString());
            
            for (WatchEvent<?> event : key.pollEvents()) {
                if(event.context().toString().contains(".dat")){
                
                    System.out.println("FileName: "+event.context());
            
                }
            }
            key.reset();
        }

        watchService.close();
    }

}

my code is waiting for the execution of that line, is it possible to somehow stop the execution, tried:

 key.cancel();
 watchService.close()

but this did not give any result, can you tell me how to solve this problem?

Answer 1

The take() method of java.nio.WatchService is defined to wait undeterminedly until a watched-for event occurs. So there is no way to "stop" it.

If you do not want to wait for an undetermined time, you can use poll() , which returns immediately, or poll(long timeout, TimeUnit unit) which returns after the specified time or when an event occurs, whatever happens first.

The most 'natural' place to run such a watcher service would be a background thread, so that the program can proceed while the watcher is waiting for the seeked event. The Callable / Future classes make a good candidate to use here. When the watcher is running in a Thread or Future , the main program could "stop" it by using Thread.interrupt() or Future.cancel() .

And be sure to join or daemonize the threads you create, otherwise your program will not finish.