java关于日期的一些常用方法总结

public class DateUtil {

	//泽勒一致性公式计算星期几
	public static String getWeekOfDate(int year, int month, int day) {
		int q = day;
		int m;
		String weekday[] = new String[] { "Saturday", "Sunday", "Monday",
				"Tuesday", "Wednessday", "Thursday", "Friday" };
		switch (month) {
		case 1:
			m = 13;
			year = year - 1;
			break;
		case 2:
			m = 14;
			year = year - 1;
			break;
		default:
			m = month;
			break;
		}
		int j = year / 100;
		int k = year % 100;
		int h = (q + 26 * (m + 1) / 10 + k + k / 4 + j / 4 + 5 * j) % 7;
		return weekday[h];
	}

	//计算两个时间段之间的星期数
	public static Object countTwoDayWeek(String startDate, String endDate) {
		if (StringUtils.isNotEmpty(startDate)
				&& StringUtils.isNotEmpty(endDate)) {
			long between_days=getDaysBetweenDates(startDate, endDate);
			Double days = Double.parseDouble(String.valueOf(between_days));
			if ((days / 7) > 0 && (days / 7) <= 1) {
				// 不满一周的按一周算
				return 1;
			} else if (days / 7 > 1) {
				int day = days.intValue();
				if (day % 7 > 0) {
					return day / 7 + 1;
				} else {
					return day / 7;
				}
			} else if ((days / 7) == 0) {
				return 0;
			} else {
				// 负数返还null
				return null;
			}
		}
		return null;
	}

	//计算两个时间段的天数
	public static long getDaysBetweenDates(String startDate, String endDate) {
		if (StringUtils.isNotEmpty(startDate)
				&& StringUtils.isNotEmpty(endDate)) {
			DateFormat ft = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			Date start = null;
			Date end = null;
			try {
				start = ft.parse(startDate);
				end = ft.parse(endDate);
			} catch (ParseException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			Calendar cal = Calendar.getInstance();
			cal.setTime(start);
			long time1 = cal.getTimeInMillis();
			cal.setTime(end);
			long time2 = cal.getTimeInMillis();
			long between_days = (time2 - time1) / (1000 * 3600 * 24);
			return between_days;
		}
		return 0;
	}

	//计算两个时间段之间的月数
	public static int getMonthSpace(String startDate, String endDate) {
		DateFormat ft = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		Calendar c1 = Calendar.getInstance();
		Calendar c2 = Calendar.getInstance();
		try {
			c1.setTime(ft.parse(startDate));
			c2.setTime(ft.parse(endDate));
		} catch (ParseException e) {
			e.printStackTrace();
		}
		if (c1.getTimeInMillis() < c2.getTimeInMillis())
			return 0;
		int year1 = c1.get(Calendar.YEAR);
		int year2 = c2.get(Calendar.YEAR);
		int month1 = c1.get(Calendar.MONTH);
		int month2 = c2.get(Calendar.MONTH);
		int day1 = c1.get(Calendar.DAY_OF_MONTH);
		int day2 = c2.get(Calendar.DAY_OF_MONTH);
		// 获取年的差值 假设 d1 = 2015-8-16 d2 = 2011-9-30
		int yearInterval = year1 - year2;
		// 如果 d1的 月-日 小于 d2的 月-日 那么 yearInterval-- 这样就得到了相差的年数
		if (month1 < month2 || month1 == month2 && day1 < day2)
			yearInterval--;
		// 获取月数差值
		int monthInterval = (month1 + 12) - month2;
		if (day1 < day2)
			monthInterval--;
		monthInterval %= 12;
		return yearInterval * 12 + monthInterval;
	}

	public static void main(String[] args) {
		System.out.println(DateUtil.getWeekOfDate(2017, 9, 30));
		System.out.println(DateUtil.getDaysBetweenDates("2016-09-30 06:30:15",
				"2018-09-30 20:30:30"));
		System.out.println(DateUtil.getMonthSpace("2016-09-30 06:30:15",
				"2015-08-31 05:30:30"));
		System.out.println(DateUtil.countTwoDayWeek("2017-09-30 06:30:15",
				"2017-10-15 05:30:30"));
	}
}