Monitor subfolders with a Java watch service

Question

I am using watchKey to listen for a file change in a particular folder.

Path _directotyToWatch = Paths.get("E:/Raja");
WatchService watcherSvc = FileSystems.getDefault().newWatchService();
WatchKey watchKey = _directotyToWatch.register(watcherSvc, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);

while (true) {
    watchKey=watcherSvc.take();
    for (WatchEvent<?> event: watchKey.pollEvents()) {
        WatchEvent<Path> watchEvent = castEvent(event);
        System.out.println(event.kind().name().toString() + " " + _directotyToWatch.resolve(watchEvent.context()));
        watchKey.reset();
    }
}

It working fine for me. If I modify a file in raja folder it gives me the file name with path. But, when I put some files in subfolders like "E:/Raja/Test", it gives me only the path where I put it, not the file name.

How to get the file name?

Answer 1

The reason why you're not getting the file name created/modified inside a subfolder is given by Stephen C in his answer.

Here is a simple example of how to register directories and subdirectories to watch them for the events you are interested in:

/**
 * Register the given directory and all its sub-directories with the WatchService.
 */
private void registerAll(final Path start) throws IOException {
    // register directory and sub-directories
    Files.walkFileTree(start, new SimpleFileVisitor<Path>() {

        @Override
        public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs)
                throws IOException {
            dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
            return FileVisitResult.CONTINUE;
        }

    });

}

---

Check out the official Java Tutorials: Watching a Directory for Changes. There you can find very nice explanations and examples with the source code.

Particularly you'll be interested in this example of how to watch a directory (or directory tree) for changes to files: WatchDir.java.

The method I supplied above was taken from this example (omitting some parts for brevity).
Read the tutorial for the details.