code: public static String createTimestampedFilename(String filenamePrefix,
                                                     Date date) {
          SimpleDateFormat formatter =
                  new SimpleDateFormat(FORMAT_JOURNAL_FILENAME_TIMESTAMP);
          formatter.setTimeZone(TimeZone.getTimeZone("GMT"));
          return filenamePrefix + formatter.format(date) + "Z";
      }
docs: Create the name for a Journal file or a log file, based on the prefix and
  the current date.