code: public static String fileNameForUrl( URL contentUrl )
    {
      String fileName = null;
      Matcher matcher = FILE_NAME_PATTERN.matcher(contentUrl.getPath());
      if( matcher.find() ) {
        fileName = matcher.group(1);
      }
      return fileName;
    }
docs: Returns the content disposition file name for a url.  If a file name cannot be parsed from this url, then null
  is returned.