`LocalDateTime` serialization issue with custom-configured `LocalDateTimeSerializer`

[mklinkj]

Hello.

There was no problem specifying the date format up to version 2.15.3, but it seems like it’s not applied in version 2.16.0

Example Project (v2.15.3)

• https://github.com/mklinkj/QnA/tree/master/Jackson/jackson-local-datetime-example

Example Project Zip File (v2.15.3)

• jackson-local-datetime-example.zip

Where to change version

• https://github.com/mklinkj/QnA/blob/f488d3f3ca2ceb3b7614902545c257e9b9f06df7/Jackson/jackson-local-datetime-example/gradle.properties#L5

ObjectMapper Setting

    ObjectMapper mapper =
        new ObjectMapper()
            .registerModule(
                new JavaTimeModule()
                    .addSerializer(
                        LocalDateTime.class,
                        new LocalDateTimeSerializer(DateTimeFormatter.ofPattern("MM/dd/yyyy"))));

Run in Jackson 2.15.3

$ gradlew clean run

> Task :run
memberJson: {"name":"user00","registerDate":"12/25/2023"}

BUILD SUCCESSFUL in 2s
5 actionable tasks: 5 executed
$ 

Run in Jackson 2.16.0

$ gradlew clean run

> Task :run
memberJson: {"name":"user00","registerDate":[2023,12,25,1,2,3]}

BUILD SUCCESSFUL in 2s
5 actionable tasks: 5 executed
$ 

• ✨ The date format set in LocalDateTimeSerializer is not applied in the 2.16.0

I think it might be due to my incorrect settings… Anyway, I’ve shared it

Thank you, Have a nice day 👍

[cowtowncoder]

Ok, first of all: thank you for reporting this issue.

Second of all: I would highly recommend NOT constructing (de)serializers directly but letting JavaTimeModule do that; you can still apply pattern overrides with:

mapper.configOverride(LocalDateTime.class)
   .setFormat(JsonFormat.Value.forPattern(""MM/dd/yyyy""))

But be that as it may, the way you do things should also work.

[mklinkj]

@cowtowncoder

Hello.

I replaced the code as you replied above and confirmed that it works fine.

• commit
  • f2c3a58773562afcc1a040cf8910208aaaa359f0

Thanks. Have a nice day. 👍

[cowtowncoder]

@mklinkj Great!

I will still see if I can resolve the problem itself, but I am glad you were able to work around that.

[cowtowncoder]

Ok, I can see why this happens: 2.16 changed registration of (de)serializers in a way that would ignore anything added via JavaTimeModule.addXxx() methods -- this was not meant to be a way to add (de)serializers.

I'll have to think of how to change this; it should be doable, just not trivially simple.

[cowtowncoder]

Was quite simple in the end, fixed for 2.16.1. I assume there will be other reports for other custom registrations.

[cowtowncoder]

And there is at least #293.

[mklinkj]

Hello.

I have confirmed that the method I used before also works well in the 2.16.1-SNAPSHOT version.

• https://github.com/mklinkj/QnA/commit/26878b3b0bf6329b9eb1827d13caf13a1095674a

Thanks. Have a nice day. 👍

[cowtowncoder]

Thank you for confirming @mklinkj !

[mdindoffer]

Ok, I can see why this happens: 2.16 changed registration of (de)serializers in a way that would ignore anything added via JavaTimeModule.addXxx() methods -- this was not meant to be a way to add (de)serializers.

I'll have to think of how to change this; it should be doable, just not trivially simple.

Hey @cowtowncoder , would you mind sharing what is the intended way of registering custom de/serializers for example for java.time.Instant ? Or point me to a documentation? Jackson's docs are so fragmented that I could not find a proper unified reference on this topic. We've been hit by this bug as well, so I'd rather rewrite our code in compliance with the guidelines. Thanks.

[cowtowncoder]

@mdindoffer Ok, two pointers:

1. 2.16.1 fixes the issue, so existing usage now works again: not recommended, but supported.
2. For better way, create SimpleModule of your own (instead of, or in addition to JavaTimeModule) and add custom (de)serializers using that -- same ways you used to add them to JavaTimeModule (using methods inherited from SimpleModule, in that case)

So the only concern is that the fact that JavaTimeModule happens to be SimpleModule (in 2.x) might lead to usage that will break with 3.x (when JavaTimeModule direct implements Module and not SimpleModule).

I hope this clarifies matters.

[mdindoffer]

@cowtowncoder OK, so would you accept a PR that marks the methods as @Deprecated in JavaTimeModule? I see no point in leaving them as is, if they are not meant to be used on the JavaTimeModule.

[cowtowncoder]

The problem is that methods come from SimpleModule and are not introduced by JavaTimeModule. I guess it would be possible to add overrides, for purpose of deprecating... but not sure how valuable that'd be. Same would also (in theory) need to be done for all methods SimpleModule exposes (it is possible to call all other configuration methods).

From my perspective deprecation is no longer necessary as usage is supported (even if not recommended), including regression test verifying functioning (ability to register custom (de)serializers). And in 3.0, due to change in base class, methods are no longer exposed at all.