Javalin: How can I use Kotlinx Serialization instead of Jackson?

[wellingtoncosta]

Firstly, congratulations for the awesome project. I started using it two days ago and it is very fast and simple.

I would like to use kotlinx.serialization instead of Jackson. How can I do it?

[tipsy]

Firstly, congratulations for the awesome project. I started using it two days ago and it is very fast and simple.

Thanks!

I would like to use kotlinx.serialization instead of Jackson. How can I do it?

You can configure the JavalinJson plugin:

JavalinJson.toJsonMapper = object : ToJsonMapper {
     override fun map(obj: Any) =  { /* Your implementation here */ }
}

JavalinJson.fromJsonMapper = object : FromJsonMapper {
    override fun <T> map(json: String, targetClass: Class<T>) { /* Your implementation here */ }
}

These will then be used when calling ctx.json() or ctx.body<MyClass>().

[wellingtoncosta]

Ok. Thanks for the quick response. I'll try it.

[Freezystem]

@wellingtoncosta Have you finally achieved kotlinx serializer replacement ?

I'm stuck here:

val kotlinx = Json { coerceInputValues = true }

JavalinJson.toJsonMapper = object : ToJsonMapper {
    override fun map(obj: Any): String = kotlinx.encodeToString(obj)
}

JavalinJson.fromJsonMapper = object : FromJsonMapper {
    override fun <T> map(json: String, targetClass: Class<T>): T = kotlinx.decodeFromString(json)
}

The decodeFromString part is not working. I also tried:

JavalinJson.fromJsonMapper = object : FromJsonMapper {
    override inline fun <reified T> map(json: String, targetClass: Class<T>): T = kotlinx.decodeFromString(json)
}

but I get a warning: Override by an inline function and an error: Override by a function with reified type parameter.
I can't figure out how to implement this override.

[Welcius]

@Freezystem I am trying too as well! Have you/someone found a solution yet?

[Freezystem]

Hi @Welcius, actually no. As of today I couldn't figure it out yet.
There was a proposal for using extension function but I didn't succeed implementing it.
Hence I resort using explicit serialization/deserialization in my endpoints like so:

// first I'm declaring a serializer/deserializer config on top of my file
val kotlinx = Json {
    ignoreUnknownKeys = true
    coerceInputValues = true
    encodeDefaults = false
}
// then later in the handler I do
fun someHandler(ctx: Context): Context {
    kotlinx.decodeFromString<MyDataClass>(ctx.body())
    // do some stuff..
    // and finally
    return ctx.status(200)
            .result(kotlinx.encodeToString(res))
            .contentType("application/json")
}

It's cumbersome but it works as expected.
Once I get a little bit more time I'll eventually try to make it works properly but I'm too busy for the moment. :disappointed:
If you ever find something interesting feel free to share here or on the other issue, I'd be glad to review it with you.