If you also do

  tw.setFilter(PathFilter.create(filepath))

You don't need to do anything in the while loop.  Just execute:

  while (tw.next()) {
    // Already positioned to the file we want to touch.
    ....
  }

The DirCacheBuilderIterator knows how to manage the rest of the entries outside of the space that the PathFilter matches against and ensure they stay unaffected in the resulting DirCache.