Java: Watching a directory to move large files

I ran into the same problem today. I my usecase a small delay before the file is actually imported was not a big problem and I still wanted to use the NIO2 API. The solution I choose was to wait until a file has not been modified for 10 seconds before performing any operations on it.

The important part of the implementation is as follows. The program waits until the wait time expires or a new event occures. The expiration time is reset every time a file is modified. If a file is deleted before the wait time expires it is removed from the list. I use the poll method with a timeout of the expected expirationtime, that is (lastmodified+waitTime)-currentTime

private final Map<Path, Long> expirationTimes = newHashMap();
private Long newFileWait = 10000L;

public void run() {
    for(;;) {
        //Retrieves and removes next watch key, waiting if none are present.
        WatchKey k = watchService.take();

        for(;;) {
            long currentTime = new DateTime().getMillis();

            if(k!=null)
                handleWatchEvents(k);

            handleExpiredWaitTimes(currentTime);

            // If there are no files left stop polling and block on .take()
            if(expirationTimes.isEmpty())
                break;

            long minExpiration = min(expirationTimes.values());
            long timeout = minExpiration-currentTime;
            logger.debug("timeout: "+timeout);
            k = watchService.poll(timeout, TimeUnit.MILLISECONDS);
        }
    }
}

private void handleExpiredWaitTimes(Long currentTime) {
    // Start import for files for which the expirationtime has passed
    for(Entry<Path, Long> entry : expirationTimes.entrySet()) {
        if(entry.getValue()<=currentTime) {
            logger.debug("expired "+entry);
            // do something with the file
            expirationTimes.remove(entry.getKey());
        }
    }
}

private void handleWatchEvents(WatchKey k) {
    List<WatchEvent<?>> events = k.pollEvents();
    for (WatchEvent<?> event : events) {
        handleWatchEvent(event, keys.get(k));
    }
    // reset watch key to allow the key to be reported again by the watch service
    k.reset();
}

private void handleWatchEvent(WatchEvent<?> event, Path dir) throws IOException {
    Kind<?> kind = event.kind();

    WatchEvent<Path> ev = cast(event);
        Path name = ev.context();
        Path child = dir.resolve(name);

    if (kind == ENTRY_MODIFY || kind == ENTRY_CREATE) {
        // Update modified time
        FileTime lastModified = Attributes.readBasicFileAttributes(child, NOFOLLOW_LINKS).lastModifiedTime();
        expirationTimes.put(name, lastModified.toMillis()+newFileWait);
    }

    if (kind == ENTRY_DELETE) {
        expirationTimes.remove(child);
    }
}