How can I validate a local date time within daylight savings time?

Question

Mar 12, 2017 02:39:00 \"America/Chicago\" does not exist. When I set the date and time to this value it does not fail. The time gets set to Mar 12, 2017 0

Answer 1

Here a validation without throwing exceptions. You only need to ask the zone rules if a LocalDateTime is valid within a given timezone:

public static boolean isValid(LocalDateTime ldt, ZoneId zoneId) {
    return !zoneId.getRules().getValidOffsets(ldt).isEmpty();
}

Answer 2

Your sample doesn't throw an exception because ZonedDateTime.of(..) adjusts the date time. The javadoc states

This creates a zoned date-time matching the input local date-time as closely as possible. Time-zone rules, such as daylight savings, mean that not every local date-time is valid for the specified zone, thus the local date-time may be adjusted.

You could use ZonedDateTime#ofStrict(LocalDateTime, ZoneOffset, ZoneId) to perform the validation.

Obtains an instance of ZonedDateTime strictly validating the combination of local date-time, offset and zone ID.

This creates a zoned date-time ensuring that the offset is valid for the local date-time according to the rules of the specified zone. If the offset is invalid, an exception is thrown.

You'll first need to construct a LocalDateTime. Then you'll get the ZoneOffset for your ZoneId for that local date time. Then you can provide all three to ofStrict.

For example,

ZoneId zoneId = ZoneId.of("America/Chicago");
LocalDateTime ldt = LocalDateTime.of(2017, 3, 12, 2, 39, 0, 0);
ZoneOffset zoneOffset = zoneId.getRules().getOffset(ldt);
ZonedDateTime zdt = ZonedDateTime.ofStrict(ldt, zoneOffset, zoneId);

would throw

Exception in thread "main" java.time.DateTimeException: LocalDateTime '2017-03-12T02:39' does not exist in zone 'America/Chicago' due to a gap in the local time-line, typically caused by daylight savings
    at java.time.ZonedDateTime.ofStrict(ZonedDateTime.java:484)