java里面一些时间的计算

/** * 计算指定日期的上一天 * * @param dateTime *            日期，格式为：yyyy-MM-dd * @return */
public static String getBeforeDay(String dateTime) {
  Calendar now = Calendar.getInstance();
  SimpleDateFormat simpledate = new SimpleDateFormat("yyyy-MM-dd");
  Date date = null;
  try {
    date = simpledate.parse(dateTime);
  } catch (ParseException ex) {
    System.out.println("日期格式不符合要求：" + ex.getMessage());
    return null;
  }
  now.setTime(date);
  int year = now.get(Calendar.YEAR);
  int month = now.get(Calendar.MONTH);
  int day = now.get(Calendar.DAY_OF_MONTH) - 1;
  now.set(year, month, day);
  String time = simpledate.format(now.getTime());
  return time;
}

/** * 计算指定日期的下一天 * * @param dateTime *            日期，格式为：yyyy-MM-dd * @return */
public static String getNextDay(String dateTime) {
  Calendar now = Calendar.getInstance();
  SimpleDateFormat simpledate = new SimpleDateFormat("yyyy-MM-dd");
  Date date = null;
  try {
    date = simpledate.parse(dateTime);
  } catch (ParseException ex) {
    System.out.println("日期格式不符合要求：" + ex.getMessage());
    return null;
  }
  now.setTime(date);
  int year = now.get(Calendar.YEAR);
  int month = now.get(Calendar.MONTH);
  int day = now.get(Calendar.DAY_OF_MONTH) + 1;
  now.set(year, month, day);
  String time = simpledate.format(now.getTime());
  return time;
}
/** * 得到指定月的天数 * @param _year * @param _month * @return */
public static int getMaxDayOfMonth(int _year, int _month) {
  Calendar now = Calendar.getInstance();
  int year = 0;
  int month = 0;
  if (_month == 1) {
    year = _year - 1;
    month = 12;
  } else {
    year = _year;
    month = _month - 1;
  }
  now.set(Calendar.YEAR, year);
  now.set(Calendar.MONTH, month);

  return now.getActualMaximum(Calendar.DATE);
}

/** * 计算时间差 * * @param beginTime *            开始时间，格式：yyyy-MM-dd HH:mm:ss * @param endTime *            结束时间，格式：yyyy-MM-dd HH:mm:ss * @return 从开始时间到结束时间之间的时间差（秒） */
public static long getTimeDifference(String beginTime, String endTime) {
    long between = 0;
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

    Date end = null;
    Date begin = null;
    try { // 将截取到的时间字符串转化为时间格式的字符串     end = sdf.parse(endTime);     begin = sdf.parse(beginTime);    } catch (ParseException e) {     e.printStackTrace();    }

      between = (end.getTime() - begin.getTime()) / 1000; // 除以1000是为了转换成秒

      return between;
    }

/** * 计算时间差 * * @param time *            指定的时间，格式为：yyyy-MM-dd HH:mm:ss * @return 当前时间和指定时间的时间差（秒） */
public static long getTimeDifference(String time) {
   long between = 0;
   SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
   String systemTime = sdf.format(new Date()).toString();

   Date end = null;
   Date begin = null;
   try { // 将截取到的时间字符串转化为时间格式的字符串     end = sdf.parse(time);     begin = sdf.parse(systemTime);    } catch (ParseException e) {     e.printStackTrace();    }

      between = Math.abs(end.getTime() - begin.getTime()) / 1000; // 除以1000是为了转换成秒

      return between;
   }