Provide a way to configure KotlinSerializationJsonDecoder

It seems there isn’t a way to provide a custom Json or set config on Json for the KotlinSerializationJsonDecoder

Spring Framework 5.3.14

Workaround:

@Configuration(proxyBeanMethods = false)
class InitConfiguration {

    @ExperimentalSerializationApi
    @Bean
    fun kotlinSerializationJsonDecoder() = KotlinSerializationJsonDecoder(Json {
        explicitNulls = false
    })

}

@ExperimentalSerializationApi
@Configuration
class WebConfig(val decoder: KotlinSerializationJsonDecoder) : WebFluxConfigurer {
    override fun configureHttpMessageCodecs(configurer: ServerCodecConfigurer) {
        super.configureHttpMessageCodecs(configurer)
        configurer.defaultCodecs().kotlinSerializationJsonDecoder(decoder)
    }
}

[jamesward]

I think you are right about the unnecessary bean but I guess I was hoping for something like Jackson2ObjectMapperBuilderCustomizer which provides a nice way to customize Jackson.

[albertocavalcante]

I just realized that for what I wanted to do I had to take a different approach. I wanted to configure the kotlinx.serialization Decoder for WebClient.

I ended up with something close to this:

object KSerializationConfig {
    val json = Json {
        ignoreUnknownKeys = true
        isLenient = true
        allowSpecialFloatingPointValues = true
        useArrayPolymorphism = true
        encodeDefaults = true
        explicitNulls = false
    }
}

    @Bean
    fun apiClient() = WebClient.builder()
            .baseUrl("${apiProperties.baseUrl}/rest/api")
            .defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
            .codecs {
                val decoder = KotlinSerializationJsonDecoder(KSerializationConfig.json)
                it.defaultCodecs().kotlinSerializationJsonDecoder(decoder)
            }.build()

Based on: https://stackoverflow.com/a/66020393/12249394 and https://discuss.kotlinlang.org/t/kotlinx-serialization-with-spring-boot/16540/15