docs: public static int getPeriodDays(Date start, Date end) {
  		try {
  			start = FORMAT_DATE_.parse(FORMAT_DATE_.format(start));
  			end = FORMAT_DATE_.parse(FORMAT_DATE_.format(end));
  			Calendar cal = Calendar.getInstance();
  			cal.setTime(start);
  			long time1 = cal.getTimeInMillis();
  			cal.setTime(end);
  			long time2 = cal.getTimeInMillis();
  			long between_days = (time2 - time1) / (1000 * 3600 * 24);
  			return Integer.parseInt(String.valueOf(between_days));
  		} catch (Exception e) {
  			throw new KnifeUtilsException(e);
  		}
  	}