java根据日期获得周月

时间的工具是开发的时候用的比较多的，几乎每个项目都要特定的写一个DateHelper类来处理一些时间转换的问题

1.根据日期获得周

/** 
	* 根据日期获得星期 
	* @param date 
	*/
	public static String getWeekOfDate(Date date) {
		if (date == null) {
			return null;
		}
		String[] weekDaysCode = { "0", "1", "2", "3", "4", "5", "6" };
		Calendar calendar = Calendar.getInstance();
		calendar.setTime(date);
		int intWeek = calendar.get(Calendar.DAY_OF_WEEK) - 1;
		return weekDaysCode[intWeek];
	}

2.获得当前周的所有日期

/** 
	 * 根据日期获得所在周的日期  
	 * @param mdate 
	 * @return 
	 */
	public static List dateGetWeek(Date date) {
		if (date == null) {
			return null;
		}
		int weekday = Integer.parseInt(getWeekOfDate(date));
		if (weekday == 0) {
			weekday = 7;
		}
		Date fdate;
		List list = new ArrayList();
		Long fTime = date.getTime() - weekday * 24 * 3600000;
		for (int i = 1; i <= 7; i++) {
			fdate = new Date();
			fdate.setTime(fTime + (i * 24 * 3600000));
			list.add(i - 1, fdate);
		}
		return list;
	}

3.判断两天是否在一天

/** 
	 * 判断两个日期是否在同一周(比较所在周的第一天是否相同)
	 * @param mdate 
	 * @return 
	 */
	public static boolean compare2dateIn1week(Date d1, Date d2) {
		if (d1 == null || d2 == null) {
			return false;
		}
		d1 = getFistWeekDay(d1) == null ? null : getFistWeekDay(d1);
		d2 = getFistWeekDay(d2) == null ? null : getFistWeekDay(d2);
		if (d1 != null && d2 != null) {
			if (DateUtil.Date2String(d1, "yyyy-MM-dd").equals(DateUtil.Date2String(d2, "yyyy-MM-dd"))) {
				return true;
			} else {
				return false;
			}
		} else {
			return false;
		}
	}

4.根据日期获得下一天  

/** 
	 * 根据日期获得下一天  
	 * @param mdate 
	 * @return 
	 */
	public static Timestamp getNextDay(Date date) {
		if (date == null) {
			return null;
		}
		Long fTime = date.getTime() + 1 * 24 * 3600000;
		return new Timestamp(fTime);
	}

5.根据日期获得一个月的第一天

/** 
	 * 根据日期获得一个月的第一天
	 * @param mdate 
	 * @return 
	 */
	public static Timestamp getMonthFirstDay(Timestamp now) {
		if (now == null) {
			return null;
		}
		Calendar monthCalendar = Calendar.getInstance();
		monthCalendar.setTime(now);
		int year = monthCalendar.get(Calendar.YEAR);
		int month = monthCalendar.get(Calendar.MONTH) + 1;
		String monthFirstDay = year +"-" + month +"-1";
		return string2TimeStamp(monthFirstDay,"yyyy-M-d");
	}

6.获得一周的第一天

/** 
	 * 根据日期获得所在周的第一天比如2013-4-10 周三  得到2013-4-8（周一）
	 * @param mdate 
	 * @return 
	 */
	public static Timestamp getFistWeekDay(Date date) {
		if (date == null) {
			return null;
		}
		int weekday = Integer.parseInt(getWeekOfDate(date));
		if (weekday == 0) {
			weekday = 7;
		}
		Long fTime = date.getTime() - (weekday - 1) * 24 * 3600000;
		return new Timestamp(fTime);
	}

7.间隔日期

/**
	 * 间隔日期
	 */
	public static int internal(Timestamp a, Timestamp b) {
		if (a == null || b == null) {
			return -1;
		}
		return Long.valueOf((a.getTime() - b.getTime()) / (24 * 3600000)).intValue();
	}

8.timestamp 转换为date

 public static Date timestampToDate(Timestamp tt) {
        return new Date(tt.getTime());
    }