Converting java.time to Calendar

java, java-time

Solution

Getting a `Calendar` instant from `ZonedDateTime` is pretty straight-forward, provided you know that there exists a `GregorianCalendar#from(ZonedDateTime)` method. There was a discussion in Threeten-dev mail group, about why that method is not in `Calendar` class. Not a very deep discussion though.

However, there is no direct way to convert from an `Instant` to `Calendar`. You've to have an intermediate state for that:

Instant instant = Instant.now();
ZonedDateTime zdt = ZonedDateTime.ofInstant(instant, ZoneId.systemDefault());
Calendar cal1 = GregorianCalendar.from(zdt);

This is probably because, as evident from the table on this oracle tutorial, an `Instant` maps to `Date` rather than a `Calendar`. Similarly, a `ZonedDateTime` maps to a `Calendar`.

Problem

What is the simplest way of getting a `Calendar` object from a `java.time.Instant` or `java.time.ZonedDateTime`?

Original source