Determine future timezone transitions

Question

I need to predict when the next at least 2 timezone transitions will be for a particular timezone.

Java 8 offers the new java.time API, specifically java.time.zone. ZoneRules.getTransitions() looks like exactly what I need however it doesn't list anything beyond the year 2010 for "Australia/Sydney".

What is the most reliable way to determine the next 2 timezone transition's date/time/offset?

Answer 1

The method ZoneRules.getTransitions() doesn't list all transitions until infinity into the future (obviously). This gets the next two transitions:

ZoneId zoneId = ZoneId.of("Australia/Sydney");
ZoneRules rules = zoneId.getRules();

ZoneOffsetTransition nextTransition = rules.nextTransition(Instant.now());
System.out.println("Next transition at: " +
        nextTransition.getInstant().atZone(zoneId));

ZoneOffsetTransition nextNextTransition =
        rules.nextTransition(nextTransition.getInstant());
System.out.println("Next transition after that at: " +
        nextNextTransition.getInstant().atZone(zoneId));

Output:

Next transition at: 2016-10-02T03:00+11:00[Australia/Sydney]

Next transition after that at: 2017-04-02T02:00+10:00[Australia/Sydney]