What is the simplest way of getting a Calendar object from a java.time.Instant or java.time.ZonedDateTime?
Calendar
java.time.Instant
java.time.ZonedDateTime
How about GregorianCalendar.from(ZonedDateTime.ofInstant(instant, zoneId))?
GregorianCalendar.from(ZonedDateTime.ofInstant(instant, zoneId))