java关于时间的相关操作

     /**
      * 获取当天时间零点
      * @return
      */
     public Date gettoday(){
         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
         String day = sdf.format(new Date());
         Date today = null;
        try {
            today = sdf.parse(day);
        } catch (ParseException e) {
            e.printStackTrace();
        }
         return today;
     }

        /**
         * 时间转字符串（20181117）
         * @param time
         * @return
         */
        public String datetostring(Date time){
            //设置要获取到什么样的时间
            SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
            //获取String类型的时间
            String createdate = sdf.format(time);
            return createdate;
        }

        /**
         * 日期增加天数
         * @param date
         * @param num
         * @return
         */
         public Date addDay(Date date, int num) {
             Calendar startDT = Calendar.getInstance();
             startDT.setTime(date);
             startDT.add(Calendar.DAY_OF_MONTH, num);
             return startDT.getTime();
            }

         /**
          * 两日期相差天数
          * @param date1
          * @param date2
          * @return
          */
         public int getday(Date date1,Date date2){
                 Calendar cal1 = Calendar.getInstance();
                cal1.setTime(date1);
                Calendar cal2 = Calendar.getInstance();
                cal2.setTime(date2);
                int day1= cal1.get(Calendar.DAY_OF_YEAR);
                int day2 = cal2.get(Calendar.DAY_OF_YEAR);
                return day2-day1;
         }