private static void saveTrackingData(TrackingData td) {
    String s = Jsons.toJson(td);

    Writer r = null;
    try {
      log.info("ADD: " + s);

      File file = new File(getTrackingFile(Calendar.getInstance()));
      r = new OutputStreamWriter(new FileOutputStream(file, true), Charsets.UTF_8);
      r.append(s);
      r.append(Streams.LINE_SEPARATOR);
    } catch (IOException e) {
      log.error("Failed to save " + s, e);
    } finally {
      Streams.safeClose(r);
    }
  }