Try this:
Date date = new Date(logEvent.timeSTamp);
DateFormat formatter = new SimpleDateFormat("HH:mm:ss.SSS");
formatter.setTimeZone(TimeZone.getTimeZone("UTC"));
String dateFormatted = formatter.format(date);
See SimpleDateFormat for a description of other format strings that the class accepts.
See runnable example using input of 1200 ms.