java日期间隔

       /**
* Date与Date之间的间隔小时数
*
* @param firstDay
*            (yyyy-MM-dd HH:mm:ss)
* @param lastDay
*            (yyyy-MM-dd HH:mm:ss)
* @return
*/
public static long countHoursBetween(Date firstDay, Date lastDay) {
long betweenHours = 1;
if (null == firstDay || null == lastDay) {
return betweenHours;
}

Calendar c1 = Calendar.getInstance();
Calendar c2 = Calendar.getInstance();
c1.setTime(firstDay);
c2.setTime(lastDay);
// 保证第二个时间一定大于第一个时间
if (c1.after(c2)) {
c1 = c2;
c2.setTime(firstDay);
}

long milles = c2.getTimeInMillis()-c1.getTimeInMillis();
betweenHours = milles/1000/3600;

return betweenHours;
}

       /**
* Date与Date之间的间隔天数
*
* @param firstDay
*            (yyyy-MM-dd HH:mm:ss)
* @param lastDay
*            (yyyy-MM-dd HH:mm:ss)
* @return
*/
public static long countDaysBetween(Date firstDay, Date lastDay) {
long betweenDays = 0;
if (null != firstDay || null != lastDay) {
betweenDays = countHoursBetween(firstDay,lastDay) / 24;
}

return betweenHours;
}