ZonedDateTime and toLocalDate / toLocalTime

#java #time

I need to deal with New York, London and Tokyo time zone in the same application. Some time it is quite difficult to manage.

This is how I convert ZonedDateTime to LocalDate. In functionOne, you can't guarantee the timezone of parameter dateTime is the one you expect. Before you convert to LocalDate, you always need to change the timezone first.

void functionOne(ZonedDateTime dateTime) {
    var date = dateTime.withZoneSameInstance(londonZoneId).toLocalDate();
    // use the date
}

If they provide a function ZonedDateTime.toLocalDate(ZoneId zoneId), it would be less error prone I think. It can force people to provide a ZoneId when they get the LocalDate.

This is another solution I can think of. We create a date time type for each timezone.

class LondonDateTime {
  private final ZonedDateTime dateTime;

  public LondonDateTime(ZonedDateTime dateTime) {
    this.dateTime = dateTime.withZoneSameInstance(londonZoneId);
  }

  public ZonedDateTime getDateTime() { return dateTime; }

  public LocalDate getLocalDate() { return dateTime.getLocalDate(); }
}

void functionTwo(LondonDateTime dateTime) {
  var date1 = dateTime.getDateTime().toLocalDate();
  // or 
  var date2 = dateTime.toLocalDate();
}