1.获取当前时间：
LocalDate now = LocalDate.now();
2.本月第一天：
LocalDate firstDayOfCurrentMouth = now.dayOfMonth().withMinimumValue();
3.本月最后天一天：
LocalDate lastDayOfCurrentMouth = now.dayOfMonth().withMaximumValue();
4.上个月的最后一天：
LocalDate lastDayOfPreviousMonth = now.minusMonths(1).dayOfMonth().withMaximumValue();
5.下个月的第一天：
LocalDate firstDayOfNextMouth = now.plusMonths(1).dayOfMonth().withMinimumValue();