How to Configure Kotlinx Serialization in Spring Boot MVC Rest Client

plugins {
    ...
    kotlin("plugin.serialization") version "2.1.0"
}

dependecies {
    ...
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.8.0")
}

import kotlinx.serialization.json.Json
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.http.MediaType
import org.springframework.http.converter.KotlinSerializationStringHttpMessageConverter
import org.springframework.http.converter.json.KotlinSerializationJsonHttpMessageConverter

@Configuration
class KtxConfig {

    @Bean
    fun ktxMessageConverter() : KotlinSerializationJsonHttpMessageConverter {
        // if you want to ignore unknown keys from json string,
        // otherwise make sure your data class has all json keys.
        val json = Json { ignoreUnknownKeys = true }
        return KotlinSerializationJsonHttpMessageConverter(json)
    }

    @Bean
    fun ktxMessageConverterWithMediaType() : KotlinSerializationStringHttpMessageConverter<Json> {
        // if you want to ignore unknown keys from json string,
        // otherwise make sure your data class has all json keys.
        val json = Json { ignoreUnknownKeys = true }
        return object : KotlinSerializationStringHttpMessageConverter<Json>(json, MediaType.TEXT_HTML, MediaType("text", "html")){}
    }

}

import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
data class ZipCode(
    @SerialName("cep")
    val zipCode: String,
    @SerialName("logradouro")
    val street: String,
    @SerialName("uf")
    val stateAcron: String,
    @SerialName("estado")
    val state: String,
    @SerialName("regiao")
    val region: String,
)

import com.ktxserializationrestclientspringboot.beans.KtxConfig
import com.ktxserializationrestclientspringboot.json.ZipCode
import org.springframework.stereotype.Component
import org.springframework.web.client.RestClient


@Component
class ViaCepGateway(
    private val ktxConfig: KtxConfig
) : ZipCodeGateway {

    private val restClient: RestClient = RestClient.builder()
        .messageConverters {
            it.add(0, ktxConfig.ktxMessageConverter())
            it.add(1, ktxConfig.ktxMessageConverterWithMediaType())
        }
        .baseUrl("https://viacep.com.br/ws/")
        .build()


    override fun getInfoCep(cep: String): ZipCode? {
        return restClient.get()
            .uri("/{cep}/json", cep)
            .retrieve()
            .onStatus({ it.is4xxClientError || it.is5xxServerError }, {_, response ->
                throw RuntimeException("Fail to find $cep informations. status code: ${response.statusCode}")
            })
            .body(ZipCode::class.java)
    }
}

.messageConverters {
    it.add(0, ktxConfig.ktxMessageConverter())
    //it.add(1, ktxConfig.ktxMessageConverterWithMediaType())  only one is needed
}

@Component
class MainCommandLineRunner(
    private val getCep: GetZipCode
): CommandLineRunner {

    private companion object {
        val logger: Logger = LoggerFactory.getLogger(MainCommandLineRunner::class.java)
    }

    override fun run(vararg args: String?) {
        val zipCodeInfo = getCep.execute("01001000")
        logger.info(zipCodeInfo.toString())
    }
}

ZipCode(zipCode=01001-000, street=Praça da Sé, stateAcron=SP, state=São Paulo, region=Sudeste)

return restClient.get()
...
.body(object : ParameterizedTypeReference<List<YOUR_CLASS>>() {})