从当前日期算起，获取几天前的日期和几个月前的日期

	/**
	 * 从当前日期算起，获取N天前的日期（当前日不算在内），日期格式为yyyy-MM-dd
	 * 
	 * @param daily 天数
	 * @return 
	 */
	public static String getDateByDay(Integer daily) {
		Date date = new Date();
		int year = Integer.parseInt(new SimpleDateFormat("yyyy").format(date));
		int month = Integer.parseInt(new SimpleDateFormat("MM").format(date));
		int day = Integer.parseInt(new SimpleDateFormat("dd").format(date)) - daily;
		if (day < 1) {
			month -= 1;
			if (month == 0) {
				year -= 1;
				month = 12;
			}
			if (month == 4 || month == 6 || month == 9 || month == 11) {
				day = 30 + day;
			} else if (month == 1 || month == 3 || month == 5 || month == 7
					|| month == 8 || month == 10 || month == 12) {
				day = 31 + day;
			} else if (month == 2) {
				if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) {
					day = 29 + day;
				}
				else {
					day = 28 + day;
				}
			}

		}
		String y = year + "";
		String m = "";
		String d = "";
		if (month < 10) {
			m = "0" + month;
		} else {
			m = month + "";
		}
		if (day < 10) {
			d = "0" + day;
		} else {
			d = day + "";
		}
		return y + "-" + m + "-" + d;
	}

	/**
	 * 从当前日期算起，获取N个月前的日期，日期格式为yyyy-MM-dd
	 * 
	 * @param mon 月份
	 * @return
	 */
	public static String getDateByMonth(Integer mon) {
		Date date = new Date();
		int year = Integer.parseInt(new SimpleDateFormat("yyyy").format(date));
		int month = Integer.parseInt(new SimpleDateFormat("MM").format(date)) - mon;
		int day = Integer.parseInt(new SimpleDateFormat("dd").format(date));
		if (month == 0) {
			year -= 1;
			month = 12;
		} else if (day > 28) {
			if (month == 2) {
				if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0)) {
					day = 29;
				} else {
					day = 28;
				}
			} else if ((month == 4 || month == 6 || month == 9 || month == 11)
					&& day == 31) {
				day = 30;
			}
		}
		String y = year + "";
		String m = "";
		String d = "";
		if (month < 10) {
			m = "00" + month;
		} else {
			m = month + "";
		}
		if (day < 10) {
			d = "0" + day;
		} else {
			d = day + "";
		}
		return y + "-" + m + "-" + d;
	}