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[Kotlin] Instant v.s. LocalDatetime

tl;dr​

Instant and LocalDateTime are two entirely different animals: One represents a moment, the other does not.

Instant represents a moment, a specific point in the UTC timeline. It elapsed from the standard Java epoch(beginning of time in Java) of 1970-01-01T00:00:00Z.

LocalDateTime represents a date and a time-of-day. But lacking a time zone or offset-from-UTC, this class cannot represent a moment. It represents potential moments along a range of about 26 to 27 hours, the range of all time zones around the globe. A LocalDateTime value is inherently ambiguous.

print(time.toInstant(ZoneOffset.UTC)) // 2023-03-22T08:25:10.195027Z.
print(time.toInstant(ZoneOffset.of("+08:00"))) 2023-03-22T16:25:10.195027Z

toInstant​

If you want to transform LocalDateTime to Instant, you have to provide the zone offset, like:

user.createdAt?.toInstant(ZoneOffset.UTC)

Reference​