Spring Boot - Custom JsonDeserializer is ignored

Question

I am trying to apply a custom Jackson deserializer (class "com.fasterxml.jackson.databind.JsonDeserializer") to a bean from a third-party library that requires custom deserialization. My custom deserializer is written in Kotlin:

@JsonComponent
class CustomDeserializer: JsonDeserializer<ThirdPartyBean> {

    constructor(): super() {
        println("CustomDeserializer registered")
    }

    override fun deserialize(parser: JsonParser?, context: DeserializationContext?): ThirdPartyBean? {
        // Custom deserialization
    }

    override fun handledType(): Class<*> {
        return ThirdPartyBean::class.java
    }
}

I have tried to do all of the following (and in fact all combinations thereof):

Use the class as-is: I can see that the deserializer is picked up - I can see the "CustomSerializer registered" being printed.
Annotate the field that uses the ThirdPartyBean with the custom deserializer (see below)
Explicitly register the Deserializer with the ApplicationContext (see below)

Ad 2:

@JsonDeserialize(using = CustomDeserializer::class)
fun getThirdPartyBean(): ThirdPartyBean = thirdPartyBean

Ad 3:

@Bean
fun jacksonBuilder(): Jackson2ObjectMapperBuilder {
    return Jackson2ObjectMapperBuilder()
        .deserializers(CustomDeserializer())
}

Regardless of what I have tried, I always get this client-side error when attempting to serialize a bean that - among other properties - contains a property of type "ThirdPartyBean":

    org.springframework.core.codec.CodecException: Type definition error: [simple type, class com.example.ThirdPartyBean]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `com.example.ThirdPartyBean` (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

Spring Boot version is 2.3.1. I am at wits end on how to solve this, any help is appreciated.

score 0 · Accepted Answer · answered Feb 09 '21 at 14:34

I have managed to solve this on my own. However I'm pretty sure there must/should be a much simpler solution, so I'm happy to hear any suggestions. I solved the problem by manually registering a Jackson module that contains my CustomDeserializer in the WebClient setup:

@SpringBootApplication
@EnableWebFlux
class MyApplication: WebFluxConfigurer {

    @Autowired
    private lateinit var objectMapper: ObjectMapper

    @Bean
    fun webClient(): WebClient {
        val customDeserializerModule = SimpleModule()

        customDeserializerModule.addDeserializer(ThirdPartyBean::class.java, CustomDeserializer())
        objectMapper.registerModule(customDeserializerModule)

        return WebClient
            .builder()
            .codecs { it.defaultCodecs().jackson2JsonDecoder(Jackson2JsonDecoder(objectMapper)) }
            .build()
    }
}

Spring Boot - Custom JsonDeserializer is ignored

1 Answers1