code: synchronized public static String getHeaderDate(long time) {
  
          if (HEADER_DEFAULT.getTimeZone() != GMT_TIMEZONE) {
              // ensure GMT is used as time zone for the header generation
              HEADER_DEFAULT.setTimeZone(GMT_TIMEZONE);
          }
  
          return HEADER_DEFAULT.format(new Date(time));
      }
docs: Returns a formated date and time String form a timestamp value based on the
  HTTP-Header date format.<p>
  
  @param time the time value to format as date
  @return the formatted date