为什么 OffsetDateTime 序列化/反序列化结果有差异？

Question

I make OffsetDateTime object follows way:

LocalDate date = LocalDate.of(2021, Month.OCTOBER, 22);
OffsetDateTime dateTime = date.atTime(OffsetTime.MAX);

I get after serialization in json:

2021-10-21T23:59:59.999999999-18:00

And after deserialization I get follow value:

2021-10-22T17:59:59.999999999Z

Why did this happen?

Why does the Z appear instead of time zone? Why is the date changed from 2021-10-21 to 2021-10-22 ?

Answer 1

What we know so far

1. You are creating an OffsetDateTime from a LocalDate adding the maximum offset available (which happens to be -18:00 hours)
2. this OffsetDateTime gets correctly serialized to a JSON value of 2021-10-21T23:59:59.999999999-18:00
3. when deserialized, the value (as String ) is 2021-10-22T17:59:59.999999999Z

The critical part is not included so far: What happens between 2. and 3.?
Please consider updating your question with everything you know about it.

What we can derive

The values that appear incongruent are basically the same moment in time ( Instant ), but represented at an offset of -18:00 at serialization and represented in UTC ( +00:00 or simply Z ). Due to a difference of 18 hours between those moments and due to the fact you created an OffsetDateTime with OffsetTime.MAX (which is 23:59:59.999999999-18:00 , the maximum time of day at an offset of -18:00 ).

That's why the result you get after deserialization is not wrong , but its representation may not be the desired one.

My guess is that an Instant is used at the sub-steps between 2. and 3. and the deserialization simply provides date and time in UTC only.

I wouldn't pass any time with a maximum offset to any API if it is not explicitly required. Is it in your situation? Consider adding information about that, too.

What we can do to make the time String s equal

You can use a different possibility of creating the OffsetDateTime from the LocalDate , that is using the maximum time of day without an offset explicitly at UTC:

OffsetDateTime dateTime = OffsetDateTime.of(date, LocalTime.MAX, ZoneOffset.UTC);

This would serialize to 2021-10-21T23:59:59.999999999Z , you could also represent it as 2021-10-21T23:59:59.999999999+00:00 or similar (I would stick to Z ) and deserialization should return the same value.