[java] How to convert milliseconds to "hh:mm:ss" format?

Test results for the 4 implementations

Having to do a lot of formatting for huge data, needed the best performance, so here are the (surprising) results:

for (int i = 0; i < 1000000; i++) { FUNCTION_CALL }

Durations:

• combinationFormatter: 196 millis
• formatDuration: 272 millis
• apacheFormat: 754 millis

• formatTimeUnit: 2216 millis

  public static String apacheFormat(long millis) throws ParseException {
      return DurationFormatUtils.formatDuration(millis, "HH:mm:ss");
  }
  
  public static String formatTimeUnit(long millis) throws ParseException {
  String formatted = String.format(
          "%02d:%02d:%02d",
          TimeUnit.MILLISECONDS.toHours(millis),
          TimeUnit.MILLISECONDS.toMinutes(millis)
                  - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis)),
          TimeUnit.MILLISECONDS.toSeconds(millis)
                  - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis)));
      return formatted;
  }
  
  public static String formatDuration(final long millis) {
      long seconds = (millis / 1000) % 60;
      long minutes = (millis / (1000 * 60)) % 60;
      long hours = millis / (1000 * 60 * 60);
  
      StringBuilder b = new StringBuilder();
      b.append(hours == 0 ? "00" : hours < 10 ? String.valueOf("0" + hours) : 
      String.valueOf(hours));
      b.append(":");
      b.append(minutes == 0 ? "00" : minutes < 10 ? String.valueOf("0" + minutes) :     
      String.valueOf(minutes));
      b.append(":");
      b.append(seconds == 0 ? "00" : seconds < 10 ? String.valueOf("0" + seconds) : 
      String.valueOf(seconds));
      return b.toString();
  }
  
  public static String combinationFormatter(final long millis) {
      long seconds = TimeUnit.MILLISECONDS.toSeconds(millis)
              - TimeUnit.MINUTES.toSeconds(TimeUnit.MILLISECONDS.toMinutes(millis));
      long minutes = TimeUnit.MILLISECONDS.toMinutes(millis)
              - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(millis));
      long hours = TimeUnit.MILLISECONDS.toHours(millis);
  
      StringBuilder b = new StringBuilder();
      b.append(hours == 0 ? "00" : hours < 10 ? String.valueOf("0" + hours) : 
      String.valueOf(hours));
      b.append(":");
      b.append(minutes == 0 ? "00" : minutes < 10 ? String.valueOf("0" + minutes) : 
      String.valueOf(minutes));
          b.append(":");
      b.append(seconds == 0 ? "00" : seconds < 10 ? String.valueOf("0" + seconds) : 
      String.valueOf(seconds));
      return b.toString(); 
   }