java获取日期之间天数的方法

private int daysBetween(Date now, Date returnDate) {
  Calendar cNow = Calendar.getInstance();
  Calendar cReturnDate = Calendar.getInstance();
  cNow.setTime(now);
  cReturnDate.setTime(returnDate);
  setTimeToMidnight(cNow);
  setTimeToMidnight(cReturnDate);
  long todayMs = cNow.getTimeInMillis();
  long returnMs = cReturnDate.getTimeInMillis();
  long intervalMs = todayMs - returnMs;
  return millisecondsToDays(intervalMs);
}
private int millisecondsToDays(long intervalMs) {
  return (int) (intervalMs / (1000 * 86400));
}
private void setTimeToMidnight(Calendar calendar) {
  calendar.set(Calendar.HOUR_OF_DAY, 0);
  calendar.set(Calendar.MINUTE, 0);
  calendar.set(Calendar.SECOND, 0);
}