Freemarker printing dates in different timezones

Question

I'm using Freemarker Version 2.3.20.

I have a data structure where two dates are contained - one in local time and one in utc time.

// 2017-07-17 18:30 UTC
ZonedDateTime utcTime = ZonedDateTime.of(2017, 7, 17, 18, 30, 0, 0, ZoneId.of("UTC"));
// 2017-07-17 20:30 (+02:00)
ZonedDateTime localTime = utcTime.withZoneSameInstant(ZoneId.of("Europe/Berlin"));

Freemarker can handle only java.util.Date so I'm handing over dates.

Map<String, Object> mapping = new HashMap<String, Object>();
mapping.put("departureTimeLocal", Date.from(localTime.toInstant()));
mapping.put("departureTimeUtc", Date.from(utcTime.toInstant()));

In my template I would expect to write something like:

Departure (local): ${departureTimeLocal?string['HH:mm']}
Departure (UTC)  : ${departureTimeUtc?string['HH:mm']}

And as a result I would like to see:

Departure (local): 20:30
Departure (UTC)  : 18:30

What I see currently is:

Departure (local): 20:30
Departure (UTC)  : 20:30    <#-- timestamp interpreted in local time -->

I've also tried something like:

Departure (converted): ${(departureTimeLocal?string['yyyy-MM-dd HH:mm'] + ' UTC')?datetime['yyyy-MM-dd HH:mm z']?string['HH:mm']}
--> Departure (converted): 22:30

What would be the best way to archive something like that?

Yes I know: java.util.Date does not really have a timezone (only for printing) and localTime/utcTime.toInstant() both map to the same instants in zulu time.

Answer 1

With freemarker 2.3.20, you can use the iso date built-in:

${departureTimeUtc?time?iso_utc_m_nz}

This built-in is deprecated since freemarker 2.3.21, and replaced by:

${departureTimeUtc?time?string.iso_m_nz_u}

The meaning of iso_m_nz_u is:

• iso: use ISO 8601:2004 format
• m: accuracy to the minute
• nz: no timezone
• u: use UTC instead of default timezone

A complete list of options can be found here.