求最近30的起始日期

/**
* 获最近30天的起始日期 输出：20160129151106 20160228151106
*/
public Map<String, Object> getRecent30Day() {

      Date today = new Date();
      long todayTimeStamp = today.getTime();
      long day30 = 30*1000*60*60*24l;
      long day30TimeStamp = todayTimeStamp - day30;

      SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmss");
      String day30Date = sdf.format(new Date(day30TimeStamp));
      String todayDate = sdf.format(new Date());

      //取当前月
      Map<String, Object> firstAndEndDayMap = new HashMap<String, Object>();
      firstAndEndDayMap.put("firstDay", day30Date);
      firstAndEndDayMap.put("endDay", todayDate);
      logger.debug("===============30天前的日期是=========="+day30Date); //20160129151106
      logger.debug("===============今天的日期是=========="+todayDate); //20160228151106
      return firstAndEndDayMap;
}