Java中得到两个不同时区下日期之间相差值

/**
  * Get relative millisecond offset of two dates in different time zones.
  * Note that the offset value is calculated as the two dates compared in a
  * same time zone.
  *
  * @param date1
  *            The first date.
  * @param timeZone1
  *            The first time zone which the first date is in.
  * @param date2
  *            The second date.
  * @param timeZone2
  *            The second time zone which the second date is in.
  * @return Millisecond offset value between the two dates. the value 0 if
  *         date2 is equal to date1; a value greater than 0 if date2 is after
  *         date1; and a value less than 0 if date2 is before date1.
  */
 public static long getDatesOffsetWithTimeZone(Date date1, TimeZone timeZone1, Date date2,
   TimeZone timeZone2)
 {
  long timeZoneOffset = timeZone2.getOffset(date2.getTime())
    - timeZone1.getOffset(date1.getTime());

  // The time millisecond offset between the two dates.
  long millisOffset = date2.getTime() - date1.getTime();

  // The relative time millisecond offset in a same time zone.
  long timeOffset = millisOffset - timeZoneOffset;

  return timeOffset;
 }