I’ve been working on a pretty easy task today (I thought it was easy at least). I want to save calender to a user then get free/busy info later from the user. All this is through java ews API

send calender

SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date startDate = formatter.parse("2014-10-14 15:00:00");
Date endDate = formatter.parse("2014-10-14 16:00:00");
appointment.setStart(startDate);
appointment.setEnd(endDate);
appointment.save();

check free/busy

SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd");
// only accurate to day, start=2014-10-14 12:00&&end=2014-10-14 13:00 is invalid
startDate = sf.parse("2014-10-14");
endDate = sf.parse("2014-10-16");
List<AttendeeInfo> attendees = new ArrayList<AttendeeInfo>();
attendees.add(new AttendeeInfo("xxx@email.com"));

GetUserAvailabilityResults results = service.getUserAvailability(
        attendees,
        new TimeWindow(startDate, endDate),
        AvailabilityData.FreeBusy);

Quite straightforward so far. However, the result is totally unexpected. The time I scheduled in the code, I saw in outlook web application, I got from free/busy API are all different! What the hell is going on here?

1. When creating appointment, timezone information needs to be set into formatter

If you set the start time to 15:00:00, it will be converted to UTC based on your jvm’s default timezone (the same as your local timezone most likely). So 15:00:00 (PST) will be converted to 22:00:00 (UTC) in this case.

THe root cause is Date only contains the millisecond value. There’s no way to set timezone to java.util.Date. However, you can use timeformatter with timezone or Calander to set timezone. The millisecond value will be recalculated according to timezone.

I misunderstood below statement in it’s documentation. “in UTC time” actually means you have to parse the date to UTC explicitly.

Time and date details that you set by using the java.util.Date class are given as UTC. When you set the date by using the Date class, make sure that it is in UTC time.

formatter.setTimeZone(TimeZone.getTimeZone(USER_TZ));

2. The returned date in free/busy info is always in UTC. You have to convert it to readable time in user’s timezone.

private static Date fromUTC(Date date, TimeZone tz) {
    return new Date(date.getTime() + tz.getOffset(date.getTime()));
}