Anyone familiar with using the Kotlin Jackson module to parse out a JSON object with nested objects? For the nested objects it seems to only work in cases where the JSON matches exactly (@JsonIgnoreProperties and configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false) do not help, though it works with the top level object). The failure is MismatchedInputException: Cannot construct instance, which I guess makes sense due to data class constructors, but is there some way to make this more flexible? Only parse the fields I need, and not break if the API returns a subset of the fields, or a new field? I'm a Kotlin newbie so just trying to figure this out as I go and any help would be appreciated.

Is there a paticular reason for using jackson instead of kotlinx.serialization or Gson?

Jackson is fast and flexible? Anyway, see #jackson-kotlin

Not sure that there is any Kotlin specific thing, described case is supported by Jackson and should work with Kotlin out of the box

I usually avoid adding the kotlin module

Also Jackson is still the fastest

I see.

@addamsson interesting - we've had the experience that GSON doesn't fail on missing non-nullable properties when deserialising. Does it definitely work for you?

@addamsson maybe I'm missing something on the config side, but here's a test case that definitely doesn't work properly:

data class Obj(val required: String)

fun main() {
    println(GsonBuilder().serializeNulls().create().fromJson("{}", Obj::class.java ))
}

the

it

?

🙂

@dave Gson was designed for java, where all reference types are nullable. It uses java reflection for deserialization, most likely. Thus, it cant possibly know unless it were somehow updated with a kotlin extension of some kind.

@Dico yeah - that's what I suspected (and is entirely reasonable). I was just curious at the statement that it worked with Kotlin. 🙂

The only way it could naturally throw the exception is if it used a setter generated by the kotlin compiler. That setter doesn't exist

TBH, for us this problem makes GSON pretty much unusable for kotlin projects, especially since Jackson and Moshi both do support blowing up when fields are missing.

What about kotlinx-serialization?

I'm not adverse to creating an http4k module for kotlinx.serialization, but not sure what features it would give at this present time over Jackson (at least for JSON and on the JVM).

i'm just speaking from my experience

@addamsson fair enough. It's all to do with usage of course. 🙃 For us it's pretty much always deserialisation of Json to data classes. Since our API is a wrapper around the JSON libs, it's easier to use the one that supports the type system.

sounds plausible

Yeah - i can see that would be attractive, although I might be worried about to much coupling between front and back end. IMHO, the multiplatform story is going to be quite a long game.

tell me about it.......

the worst thing about multiplatform atm is gradle problems imo

I agree.