So I've seen that kotlinx serialization can be use...

# spring

[Derek Ellis]

So I've seen that kotlinx serialization can be used just by adding it to the classpath, and that it only handles classes marked with @Serializable and primitive collections before forwarding everything to Jackson. I've run into an issue where I want to serialize a List (I believe the implementation is just a regular ArrayList) of a serializable class that has some @SerialName annotations on the properties, but it looks like it's being forwarded to Jackson and the @SerialName names are being ignored.
Is this functionality supported, and how would I update the configuration of my WebFlux project to use kotlinx serialization for this?

[Yevgeni Liskovich]

you can create configuration bean in which you can check if kotlinx.serialization converter is exist and in what order, if it before jackson or after it. you also can override converters with your own configuration. it should be something like this:

@Configuration
class KotlinxSerializationConfig : WebFluxConfigurer {
    override fun extendMessageConverters(converters: MutableList<HttpMessageConverter<*>>) {
       // here you can check converters list
    }
}

[Sourabh Rawat]

Remove Jackson dependency, if you don't need it specifically. Having multiple serialisation libs will give you pain sooner or later

[Derek Ellis]

Looking more at the problem, I think the issue with the list is that the kotlinx serialization encoder/decoder implementation in Spring doesn't support polymorphism yet.

[Derek Ellis]

As for removing Jackson altogether, that isn't always possible if you're using actuator or something like that, unfortunately

[Richard Gomez]

The Spring documentation for kotlinx.serialization is sparse. According to this document from Jetbrains, you need to explicitly exclude spring-boot-starter-json.

Gradle

implementation("org.springframework.boot:spring-boot-starter-web") {
   exclude(module = "spring-boot-starter-json")
}
implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.0.0")

Maven

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-json</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

[Richard Gomez]

Tangential to this issue, can someone elucidate why this works for @RestController annotated methods but not the router DSL? The latter throws an exception (posted in thread).

spring_kotlinx-serialization_kt.cpp

[Richard Gomez]

Can't attach multiple files to a message. This is part of the exception.

exception.log

[Sourabh Rawat]

I'll assume you are using Kotlin serialisation library. So you need to mark Post class with @Serializable.

[Richard Gomez]

@Sourabh Rawat: Apologies, I omitted the class declaration in my ad-hoc code snippet.

It is annotated with @Serializable in the actual code. The strange part is that it's getting serialized by kotlinx.serialization when using @RestControler, but not when using the router DSL.