工作中java常用的时间工具类：Calendar

/**

* 根据传参求出对应月份的最后一天

*/

@Test

public void setAndGetRangeEndTime() {

int index = 1;

//int range=2;

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

Calendar calendar = Calendar.getInstance();

calendar.setTime(new Date());

//昨天

calendar.set(Calendar.DATE, calendar.get(Calendar.DATE) - 1);

calendar.set(Calendar.HOUR_OF_DAY, 23);

calendar.set(Calendar.MINUTE, 59);

calendar.set(Calendar.SECOND, 59);

//月份

calendar.set(Calendar.MONTH, calendar.get(Calendar.MONTH) - index);

//月份最大天数

int maxDay = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

calendar.set(Calendar.DAY_OF_MONTH, maxDay);

String format = sdf.format(calendar.getTime());

System.out.println("结果：" + format);

}

/**

* 补全开始到结束时间的工具方法

*/

public List<String> testDateUtils(String startTime, String endTime) throws Exception {

startTime = "2021-02-03";

endTime = "2021-02-06";

if (StringUtils.isEmpty(startTime) || StringUtils.isEmpty(endTime)) {

throw new Exception("开始日期和截止日期都不能为空！");

}

//compareTo 当两者相等时为0，当前者小于后者时返回-1，大于时返回1。具体查看源码。

if (startTime.compareTo(endTime) > 0) {

throw new Exception("开始日期必须小于等于截止日期！");

}

SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");

Date startDate = simpleDateFormat.parse(startTime);

Date endDate = simpleDateFormat.parse(endTime);

Calendar startCal = Calendar.getInstance();

Calendar endCal = Calendar.getInstance();

startCal.setTime(startDate);

endCal.setTime(endDate);

List<String> days = new ArrayList<>();

//当开始时间大于结束时间时则返回

while (startCal.compareTo(endCal) <= 0) {

days.add(simpleDateFormat.format(startCal.getTime()));

//Date本身加减日期过于麻烦，使用Calendar操纵日期；开始时间+1；

startCal.add(Calendar.DATE, 1);

}

return days;

}