Watch a directory for changes using a WatchService.

DirWatcher.java

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

import static java.nio.file.StandardWatchEventKinds.*;

/**
 * Watch a directory for changes using a WatchService.
 */
public class DirWatcher {

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

        WatchService watchService = FileSystems.getDefault().newWatchService();

        Path homeDir = Paths.get(System.getProperty("user.home"));
        homeDir.register(watchService, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);

        System.out.printf("Watch service registered for: %s%n", homeDir);

        WatchKey eventKey;
        while(true) {
            try {
                eventKey = watchService.take();
            } catch (InterruptedException ie) {
                System.out.printf("Watch service interrupted!%n");
                return;
            }

            for (WatchEvent<?> event : eventKey.pollEvents()) {
                WatchEvent.Kind eventKind = event.kind();

                if (eventKind == OVERFLOW) {
                    System.out.printf("Overflow event");
                    continue;
                }

                WatchEvent<Path> specEvent = (WatchEvent<Path>)event;
                Path filename = specEvent.context();

                if (eventKind == ENTRY_CREATE) {
                    System.out.printf("CREATED %s%n", filename);
                } else if (eventKind == ENTRY_MODIFY) {
                    System.out.printf("MODIFIED %s%n", filename);
                } else if (eventKind == ENTRY_DELETE) {
                    System.out.printf("DELETED %s%n", filename);
                }
            }

            eventKey.reset();
        }
    }
}