Don't use LocalDateTime for java8 datetime mapping

[cbornet]

LocalDateTime doesn't have any time zone so it's error prone for systems that don't communicate in the same timezone.
Instant, ZonedDateTime or OffsetDateTime types should be considered instead.

[wing328]

FYI. C# already supports OffsetDateTime via CLI option

[cbornet]

Also by default, when Jackson serializes/deserializes a LocalDateTime, it uses "yyyy-MM-dd'T'HH:mm:ss.SSS" without the 'Z' or the time offset. So it is not compatible with swagger's datetime format.

[ebelanger]

#3002

I am leaving a link to this pull request and the alternative solution so that other may benefit like I did.

[cbornet]

I used Instant because:

• ZonedDateTime has time-zone info (eg. Europe/Paris) which is not supported by rfc3339
• Older implementations of date-time (eg. in java 6) may only use rfc822 time zones (-0800 instead of -08:00) so I generally prefer to force UTC at the API level. Feel free to comment if you think OffsetDateTime would be better.

[cbornet]

Just saw an issue with using Instant: we will probably not be able to deserialize rfc3339 dates with time offset (at least that's the case with Jackson).

And the issue with rfc3339 date offset not being supported is also on android implementation of SimpleDateFormat (which is more problematic than java6 in the end).
This makes me think that some of our java client implementations may have issues on android (eg. java jersey client uses the 'XXX' SimpleDateFormat to be compliant with rfc3339 but that will probably fail on android).

So to sum up:

• Instant will not deserialize rfc3339 but will serialize correctly for android (I don't know about other clients)
• OffsetDateTime will deserialize correctly but the serialized will probably not be readable by android by default and maybe other clients. Note that we can probably adapt the serializers to force the output in UTC/Zulu (it's possible with Jackson).

So I think we use OffsetDateTime and configure the serializers in the templates to output in Zulu. Ok with that ?