JAVA 日期加减

/**
	 * 计算前一天 、后一天
	 * 
	 * @param date 当前输入的日期 格式为 2010-01-21
	 * @param amount
	 * @return
	 */
	public static String getYesterday(String date, int amount) {
		String newDate = Constant.EMPTY_STRING;
		if (date != null) {
			DateFormat format = new SimpleDateFormat("yyyy-MM-dd");
			Date dd;
			try {
				dd = format.parse(date);
				Calendar calendar = Calendar.getInstance();
				calendar.setTime(dd);
				calendar.add(Calendar.DAY_OF_MONTH, amount);
				newDate = format.format(calendar.getTime());

			} catch (ParseException e) {
				e.printStackTrace();
			}

		}
		return newDate;
	}



/**
	 * 计算两天之间相差的天数 调用此方法必须保证 时间格式与 timeFormatStr指定格式一致 否则异常
	 * 
	 * @param beginDate 开始时间
	 * @param endDate 结束时间
	 * @param timeFormatStr  输入时间格式
	 * @return int 时间相差天数
	 */
	public static int getCountDays(String beginDate, String endDate, String timeFormatStr) {
		int days = 0;

		if (beginDate != null && endDate != null && timeFormatStr != null) {
			SimpleDateFormat dateFormat = new SimpleDateFormat(timeFormatStr);
			Calendar beginCalendar = Calendar.getInstance();
			Calendar endCalendar = Calendar.getInstance();

			try {
				endCalendar.setTime(dateFormat.parse(endDate));
				beginCalendar.setTime(dateFormat.parse(beginDate));
				while (beginCalendar.before(endCalendar)) {
					days++;
					beginCalendar.add(Calendar.DAY_OF_YEAR, 1);
				}
			} catch (ParseException e) {
				// 日期格式异常
				logger.error("getCountDays failed the" + beginDate + "or" + endDate + "is not format"
						+ timeFormatStr, e);
			}
		}
		return days;
	}


/** 取近期一年的数据*/
	public static List<String> getYears() {
		List<String> result = new ArrayList<String>();
		Calendar c = Calendar.getInstance();
		c.set(Calendar.YEAR, Integer.parseInt(DateUtil.getSysDate("yyyy")));
		c.set(Calendar.MONTH, Integer.parseInt(DateUtil.getSysDate("MM")));

		result.add(DateUtil.getSysDate("yyyyMM"));

		for (int i = 0; i < 11; i++) {
			c.add(Calendar.MONTH, -1);
			int y = c.get(Calendar.YEAR);
			int m = c.get(Calendar.MONTH);

			if (m == 0) {
				result.add((y - 1) + "12");
			} else {
				if (m < 10)
					result.add(y + "0" + m);
				else
					result.add(y + (m + ""));
			}
		}
		return result;
	}

	/** 取上个月 */  
	public static String getPrevMonth(String yearMonth) {
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
		Calendar calendar = Calendar.getInstance();
		Date curDate = java.sql.Date.valueOf(yearMonth + "-10");
		calendar.setTime(curDate);
		// 取得现在时间
		// System.out.println(sdf.format(curDate));

		// 取得上一个时间
		calendar.set(Calendar.MONDAY, calendar.get(Calendar.MONDAY) - 1);

		// 取得上一个月的下一天
		calendar.set(Calendar.DAY_OF_MONTH, calendar.get(Calendar.DAY_OF_MONTH) + 1);
		return sdf.format(calendar.getTime());
	}

	/** 取当月下的最后第一天 */
	public static void getLastDay(String yearMonth) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(java.sql.Date.valueOf(yearMonth + "-01"));

		cal.roll(Calendar.DAY_OF_MONTH, -1);
		System.out.println(new SimpleDateFormat("yyyy-MM-dd").format(cal.getTime()));
	}

	/** 取当月下的第一天 */
	public static void getFirstDay(String yearMonth) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(java.sql.Date.valueOf(yearMonth + "-01"));
		cal.set(Calendar.DAY_OF_MONTH, 1);
		System.out.println(new SimpleDateFormat(DEFAULT_DATE_FORMAT).format(cal.getTime()));
	}


/**
	 * 日期按小时加减
	 *  
	 */
	public static void dateByHour(int hourNumber) throws ParseException {
		
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		
		String time="2016-08-02 20:00:00";
		
		Date date=sdf.parse(time);
		long nh = 1000*60*60*hourNumber; 
		//long nh = 1000*60*60*8;//8小时的毫秒数
		
		long te=date.getTime()+nh; 
		
		sdf.format(te); //时间转换成字符
	
		sdf.parse(sdf.format(te));//字符转换成时间
		
	}