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I have a data source with joda time DateTime objects stored. I need to convert them into java ZonedDateTime objects, keeping the original timezone.

It is not sufficient to keep the offset since some DateTime objects represents daily repetitive tasks, and these tasks must occur at a specific time in a specific time zone for every date. They must thus follow the specified TimeZone transitions for example summer and winter time. I cannot tell the final usage of the DateTime objects, so I need to keep the Time Zone information on all objects to be safe.

How to convert from org.joda.time.DateTime to java.time.ZonedDateTime?

Will all

ord.joda.time.DateTimeZone.getId()

map to the id's available in

java.time.ZoneId

assylias
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Andreas Lundgren
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2 Answers2

32

You should avoid providing each field separately if you are working with daylight saving transitions. Convert using epochMillis instead, as in the following example.

Instant instant = Instant.ofEpochMilli(dt.getMillis());
ZoneId zoneId = ZoneId.of(dt.getZone().getID(), ZoneId.SHORT_IDS);
ZonedDateTime zdt = ZonedDateTime.ofInstant(instant, zoneId);

Otherwise you will lose one hour on the date of transition. For example, Germany transitioned from summer time (GMT+2) to winter time (GMT+1) on 29.10.2017 at 03:00 GMT+2, which becomes 02:00 GMT+1. On that day, you have 2 instances of 02:00 - an earlier one with GMT+2 and a later one with GMT+1.

Since you are working with ZoneIds and not with offsets, there's no way of knowing which one of the 2 instances you want. By default, the first one is assumed during conversion. Both 02:00 GMT+2 and 02:00 GMT+1 are going to be converted to 02:00 GMT+2 if you provide hourOfDay along with ZoneId.

Muhip Tezcan
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    This should be the accepted answer, it's more accurate than the currently-accepted answer and probably much more efficient too. Would your last line be equivalent to `instant.atZone(zoneId)`? – Ken Williams Jan 16 '19 at 19:18
20

Not all time-zone strings from Joda-Time will match java.time but the vast majority will as they are both based on the IANA tz data. Compare DateTimeZone.getAvailableIDs() to ZoneId.getAvailableZoneIds() to determine the mismatch. Additional identifiers can be mapped using ZoneId.of(String, Map).

To do the main conversion in the most efficient way, you have to pass in each field:

ZonedDateTime zdt = ZonedDateTime.ofLocal(
    LocalDateTime.of(
        dt.getYear(),
        dt.getMonthOfYear(),
        dt.getDayOfMonth(),
        dt.getHourOfDay(),
        dt.getMinuteOfHour(),
        dt.getSecondOfMinute(),
        dt.getMillisOfSecond() * 1_000_000),
    ZoneId.of(dt.getZone().getID(), ZoneId.SHORT_IDS),
    ZoneOffset.ofTotalSeconds(dt.getZone().getOffset(dt) / 1000));

Note the use of ZoneId.SHORT_IDS as the Map in this case.

For a simpler solution that handles most use cases, but at lower performance, use this:

ZonedDateTime zdt = dt.toGregorianCalendar().toZonedDateTime();
JodaStephen
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  • Is there a specific subset that is not in one or the other? Perhaps some of the older POSIX compatibility zones? I would hope all modern `Area/Locality` style zones would be available in both. – Matt Johnson-Pint Mar 05 '15 at 19:29
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    The only difference is ROC, which was replaced by ROK. The EST, HST and MST zones can be accessed using `ZoneId.SHORT_IDS`. Otherwise, any differences are just from the later version of the time-zone database in Joda-Time. – JodaStephen Mar 11 '15 at 11:08
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    @JodaStephen In stead of `ZoneId.of(dt.getZone().getID(), ZoneId.SHORT_IDS))` wouldn't `dt.toTimeZone().toZoneId()` work as well? it seems to leave the nitty gritty to JodaTime and Java respectively. – NomeN Mar 31 '16 at 09:38
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    This cannot work correctly around DST changes (`(year, month, day, hour, minute, second, millis, zone)` does not define a point in time). @MuhipTezcan answer seems to get this right. – Piotr Findeisen Feb 13 '18 at 09:10
  • Fixed to handle DST by passing in the offset – JodaStephen Feb 14 '18 at 09:53