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
You need to get the TimeZone using the instant and then you can get a calendar.
Calendar myCalendar = GregorianCalendar.from(ZonedDateTime.ofInstant(Instant.now(), ZoneId.systemDefault()));