Java Utililty Methods Millisecond Convert

DecimalFormat df20 = new DecimalFormat("00");
DecimalFormat df30 = new DecimalFormat("000");
Calendar c = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
c.setTimeInMillis(millis);
return new StringBuffer(12).append(df20.format(c.get(Calendar.HOUR_OF_DAY))).append(":")
        .append(df20.format(c.get(Calendar.MINUTE))).append(":").append(df20.format(c.get(Calendar.SECOND)))
        .append(".").append(df30.format(c.get(Calendar.MILLISECOND))).toString();

if (durationInMillis < 0) {
    throw new IllegalArgumentException("Duration must be greater than zero!");
return (new SimpleDateFormat("mm:ss:SSS")).format(new Date(durationInMillis));

return date2.getTime() - date1.getTime();

if (diffMillis == null) {
    return "";
long day = diffMillis / (24 * 60 * 60 * 1000);
long hour = (diffMillis / (60 * 60 * 1000) - day * 24);
long min = ((diffMillis / (60 * 1000)) - day * 24 * 60 - hour * 60);
long se = (diffMillis / 1000 - day * 24 * 60 * 60 - hour * 60 * 60 - min * 60);
StringBuilder sb = new StringBuilder();
...

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
format.setTimeZone(TimeZone.getTimeZone("GMT"));
return format.format(new Date(timeMillisecGMT));

DateFormat df = DateFormat.getDateTimeInstance();
return df.format(new Date(timestamp));

return formattor.format(new Date(millis));

SimpleDateFormat dateFormat = getDateFormat(withMilliseconds);
return dateFormat.format(new Date(time));

DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(now);
return formatter.format(calendar.getTimeInMillis());

SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
fmt.setTimeZone(TimeZone.getTimeZone("UTC"));
return fmt.format(getDateFromMillis(timeInMillis));