獲取第幾天時間的日期

  /**
	 * 獲取過去第幾天的日期
	 * 
	 * @param past
	 * @return
	 */
	public static String getPastDate(int past) {
		Calendar calendar = Calendar.getInstance(); // DAY_OF_YEAR
		calendar.set(Calendar.DAY_OF_MONTH, calendar.get(Calendar.DAY_OF_MONTH) - past);
		Date today = calendar.getTime();
		SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
		String result = format.format(today);
		return result;
	}