Java monitoring multiple folders

Question

I need to monitor multiple folder and I want to khow which folder has received an event to execute a particular treatment. I've tried this code.

WatchService watchService = FileSystems.getDefault().newWatchService();
opexFolder.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);
docupostFolder.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);

    boolean valid = true;
    do {
        WatchKey watchKey = watchService.take();
        for (WatchEvent<?> event : watchKey.pollEvents()) {
            WatchEvent.Kind kind = event.kind();                
            if (StandardWatchEventKinds.ENTRY_CREATE.equals(event.kind())) {                    
                String fileName = event.context().toString();                   

                //here I want to khow the path of the folder that has 
                // received the ENTRY event 
               String pathToExplore = ??;
              if (pathToExplore has some value) {
                treatments;
              } else {
                other treatments;
                }

            }
        }
        valid = watchKey.reset();

    } while (valid);
}

Is it possible to do that, or I must to create watchService per folder.

Thanks.

Answer 1

WatchService.take() will return a different watch key for every watched dir. And you can get the watched dir from the WatchKey::watchable() method.

So by inspecting the returned value of WatchKey::watchable() you'll know for which directory is this event.

---

Is the WatchKey usualy constant?

No. The WatchKey is not a constant. You acquire it by calling WatchKey watchKey = watchService.take(); You've already done it in the code you've posted.

How can I say this is opexFolder's key or docupostFolder's key

Just call Path directory = WatchKey::watchable()

Here is a simple example application:

import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;

public final class WatchServiceExample {

    public static void main(String[] args) throws Exception {
        //We'll use this watch service to monitor all directories we are interested in
        final WatchService watchService = FileSystems.getDefault().newWatchService();

        //We'll use this directory for the test in order not to create junk in the system
        final Path tempDirectory = Files.createTempDirectory("watch-service-example");
        System.out.println("Created temporary directory: " + tempDirectory.toAbsolutePath());

        for (int i = 0; i < 10; i++) {
            final Path watchedDir = Files.createDirectory(tempDirectory.resolve("watched_" + i));
            System.out.println("Created watched directory: " + watchedDir.toAbsolutePath());
            watchedDir.register(watchService, StandardWatchEventKinds.ENTRY_CREATE);
        }

        System.out.println("Initialization complete. When you create an entry in the watch dirs you'll be notified.");
        while (true) {
            final WatchKey watchKey = watchService.take();
            final Watchable watchable = watchKey.watchable();

            //Since we are registering only paths in teh watch service, the watchables must be paths
            if (!(watchable instanceof Path)) {
                throw new AssertionError("The watchable should have been a Path");
            }

            final Path directory = (Path) watchable;
            System.out.println("Processing events for watched directory: " + directory);

            for (WatchEvent<?> event : watchKey.pollEvents()) {
                System.out.println("Received event '"
                  + event.kind()
                  + "' for entry '"
                  + event.context()
                  + "' in watched directory '"
                  + directory + "'"
                );
            }

            if (!watchKey.reset()) {
                System.out.println("Failed to reset watch key: will not process more events");
                break;
            }
        }

        //Lets clean up after ourselves
        Files.walkFileTree(tempDirectory, new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                Files.delete(file);
                return FileVisitResult.CONTINUE;
            }

            @Override
            public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
                Files.delete(dir);
                return FileVisitResult.CONTINUE;
            }
        });
    }
}

Output from the sample application:

Created temporary directory: /tmp/watch-service-example4292865635932187600
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_0
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_1
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_2
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_3
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_4
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_5
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_6
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_7
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_8
Created watched directory: /tmp/watch-service-example4292865635932187600/watched_9
Initialization complete. When you create an entry in the watch dirs you'll be notified.
Processing events for watched directory: /tmp/watch-service-example4292865635932187600/watched_5
Received event 'ENTRY_CREATE' for entry 'test' in watched directory '/tmp/watch-service-example4292865635932187600/watched_5'
Processing events for watched directory: /tmp/watch-service-example4292865635932187600/watched_8
Received event 'ENTRY_CREATE' for entry 'test' in watched directory '/tmp/watch-service-example4292865635932187600/watched_8'