FolderWatcher.java

package modern.challenge;

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchEvent.Kind;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;

public class FolderWatcher {

    public void watchFolder(Path path) throws IOException, InterruptedException {
        try (WatchService watchService = FileSystems.getDefault().newWatchService()) {
            path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE,
                    StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_DELETE);

            System.out.println("Watching: " + path);

            //start an infinite loop
            while (true) {

                //retrieve and remove the next watch key
                final WatchKey key = watchService.take();

                //get list of pending events for the watch key
                for (WatchEvent<?> watchEvent : key.pollEvents()) {

                    //get the kind of event (create, modify, delete)
                    final Kind<?> kind = watchEvent.kind();

                    //handle OVERFLOW event
                    if (kind == StandardWatchEventKinds.OVERFLOW) {
                        continue;
                    }

                    //get the filename for the event
                    final WatchEvent<Path> watchEventPath = (WatchEvent<Path>) watchEvent;
                    final Path filename = watchEventPath.context();

                    //print it out
                    System.out.println(kind + " -> " + filename);
                }

                //reset the key
                boolean valid = key.reset();

                //exit loop if the key is not valid (if the directory was deleted, per example)
                if (!valid) {
                    break;
                }

            }
        }
    }
}