Add JsonMapper to replace generic ObjectMapper usage

[cowtowncoder]

Due to problems with trying to override builder factory for ObjectMapper, and introduction of JSON-specific format features (JsonReadFeature, JsonWriteFeature), it is necessary to introduce separate JsonMapper, to be used instead of ObjectMapper.
With this (and related Smile, CBOR additions), there will now be format-specific mapper subtype for all formats. ObjectMapper will still exist, and may even be instantiated (more so with 2.10, less with 3.x), but usage should move over to specific mappers for 3.x.

[IEnoobong]

hi @cowtowncoder , i'm wondering if there's a straight forward way to copy an already configured ObjectMapper to JsonMapper?

Use case is I have an autoconfigured ObjectMappper - Spring, and I'll like to use a JsonMapper with the same settings but add a few new ones

[JooHyukKim]

Try looking for some sort of copy method in ObjectMapper @IEnoobong

[IEnoobong]

@JooHyukKim thanks, there's one but it doesn't return a JsonMapper

[cowtowncoder]

Just cast it: return type of copy() in ObjectMapper has to be plain ObjectMapper, but if you call it on JsonMapper, it'll be copied as JsonMapper.

But also note that as things are, there is no additional functionality in JsonMapper over ObjectMapper (but there are other format-specific subtypes that obviously behave differently).

Also: if your reference is to JsonMapper, then calling copy() on it is declared to return JsonMapper.

If question is on creating JsonMapper from some other type, like CBORMapper or so; no, "format-bending" functionality does not exist, and -- although I thought about it -- won't. Seems difficult or impossible to reliable do that, considering all the things that can vary (esp. wrt modules registered).

[IEnoobong]

Thanks @cowtowncoder

I did this

  public JsonMapper httpObjectMapper() {
    var copy = (JsonMapper) objectMapper.copy();
    return copy.rebuild()
        .propertyNamingStrategy(PropertyNamingStrategies.SNAKE_CASE)
        .enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS)
        .enable(EnumFeature.WRITE_ENUMS_TO_LOWERCASE)
        .build();
  }

But getting this error

Caused by: java.lang.ClassCastException: class com.fasterxml.jackson.databind.ObjectMapper cannot be cast to class com.fasterxml.jackson.databind.json.JsonMapper (com.fasterxml.jackson.databind.ObjectMapper and com.fasterxml.jackson.databind.json.JsonMapper are in unnamed module of loader 'app')

[cowtowncoder]

Ok, please file an issue with full reproduction and I can have a look.
And make sure to include Jackson version you are using!!!

I suspect it is the rebuild() method.

Note, too, that you need NOT use copy() with rebuild() as it already makes a copy: so you'd do:

   return originalJsonMapper.rebuild()
         // make changes
        .build();

[cowtowncoder]

Cannot reproduce the issue with 2.17, fwtw.

[IEnoobong]

@cowtowncoder thanks for your response, the issue rather is JsonMapper is a subclass of ObjectMapper not a superclass hence ObjectMapper cannot be cast to JsonMapper which is what I was trying to do.

[JooHyukKim]

I see what your problem is now. I don't see direct way of copying.
Maybe we could add new JsonMapper(ObjectMapper) for such use case? 🤔
WDYT @cowtowncoder ?

[cowtowncoder]

@cowtowncoder thanks for your response, the issue rather is JsonMapper is a super class of ObjectMapper not a subclass hence ObjectMapper cannot be cast to JsonMapper which is what I was trying to do.

No. JsonMapper is a sub-class, ObjectMapper super class.
But correct, you cannot cast ObjectMapper that is not JsonMapper into JsonMapper.

Next time please include some code so we can actually evaluate what you are trying to do -- that makes misunderstandings less likely.

[cowtowncoder]

@JooHyukKim No; I thought about that in the past, but things get rather complicated quickly in 2.x, wrt configuration. It would be very difficult to ensure everything is properly copied.

We could consider this for 3.0 where things are bit cleaner as ObjectMapper subtypes are immutable.