Help with displaying Date from Unix seconds

Question

My program receives seconds taken from a Unix system and must display them on my GUI. I realize I have to convert seconds to milliseconds for the Date, plus I take into consideration the timezone.
My problem is that everything works correctly for time zones from GMT -1:00 all the way to GMT -12:00, but GMT time and all the zones between GMT +1:00 to GMT +12:00 display the wrong time. It varies how many hours off it is.
Does anyone have any suggestions? I have been searching for similar issues.
here is my code:
static public String SecToTimeOfDay(long sec)
   SimpleDateFormat  dateFormat  = new SimpleDateFormat("HH:mm:ss");
   long timeZone  = java.util.TimeZone.getDefault().getRawOffset();
   int milli = 1000;
   String date;
   if (timeZone < 0)
      timeZone = timeZone * -1;
   //convert to seconds to milliseconds
   date = dateFormat.format(new java.util.Date((sec * milli) + timeZone));
   return date;
}

Answer 1

That is not the right way to handle time zones. Try the following and see if you're still having problems.
static public String SecToTimeOfDay(long sec){  
    SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
    dateFormat.setTimeZone(java.util.TimeZone.getDefault());
    int milli = 1000;
    date = dateFormat.format(new java.util.Date(sec * milli));
    return date;
}