A simple FileSystem Indexer capable of walking through a specific Directory recursively and if configured registering all Directories on it's way to a watchdog. The watchdog then will call the indexer if a directory has been modified or created.
Java 7
To use the Indexer you can use it directly and providing it with your FileVisitor or you can use the IndexingThread for it.
Indexer indexer = new Indexer();
indexer.setVisitor(myFileVisitor);
indexer.index(myDirectory);
// if using the Thread
IndexingThread thread = new IndexingThread();
thread.setIndexer(indexer);
thread.run();