For what I can only assume is a timezone issue, the following code yields different week of year values for the same day, but different times:
Note, the code is written in Kotlin
Example
fun main(args: Array<String>) {
val middaySundayAfterEpoch = Instant.EPOCH + Duration
.ZERO
.plusDays(3)
.plusHours(12)
val almostMidnightSundayAfterEpoch = Instant.EPOCH + Duration
.ZERO
.plusDays(3)
.plusHours(23)
println(getWeekOfYear(middaySundayAfterEpoch))
println(getWeekOfYear(almostMidnightSundayAfterEpoch))
}
fun getWeekOfYear(instant: Instant): Int {
val calendar: Calendar = Calendar.getInstance()
calendar.time = Date.from(instant)
return calendar.get(Calendar.WEEK_OF_YEAR)
}
Results
1
2
Assumptions
Question
How do I modify this to ignore the time zone, so that both times occur in the same week?
You should never use the legacy java.util.Date and java.util.Calendar if you can possibly avoid them, this being one of many reasons.
The ZonedDateTime object provides a way to get this:
instant.atZone(ZoneId.of("UTC")).get(IsoFields.WEEK_OF_WEEK_BASED_YEAR)
EDIT: A previous version of this answer used the system default time, as well as ChronoUnit.ALIGNED_WEEK_OF_YEAR. This considers 1-7 January to be "week 1" of the year, regardless of on which day of the week 1 January lies in a particular year. However, it will be based on the date part of the ZonedDateTime.