code: public static Date dateIncreaseByMonth(Date date, int mnt) {
  
          Calendar cal = GregorianCalendar.getInstance();
          cal.setTime(date);
          cal.add(Calendar.MONTH, mnt);
  
          return cal.getTime();
      }
docs: 日期增加-按月增加
  
  @param date
  @param mnt
  @return java.util.Date