The java.nio.file.WatchService for Directory Monitoring in Java

WatchService API allows you to monitor a directory for changes, such as file creation, deletion, or modification, without polling.

Source Code

try (WatchService service = FileSystems.getDefault().newWatchService()) {
    Path path = Paths.get(System.getProperty("user.home"));
    path.register(service, StandardWatchEventKinds.ENTRY_CREATE);
    WatchKey key;
    while ((key = service.take()) != null) {
        for (WatchEvent event : key.pollEvents()) {
            System.out.println("Event kind:" + event.kind() 
                               + ". File affected: " + event.context() + ".");
        }
        key.reset();
    }
} catch (IOException | InterruptedException e) {
    e.printStackTrace();
}