Retrofit + Gson. Gson not calling custom deserializer

Question

class GetBusinessMapResponseDTODeserializer : JsonDeserializer<GetBusinessMapResponseDTO> {
    override fun deserialize(
        json: JsonElement?,
        typeOfT: Type?,
        context: JsonDeserializationContext?
    ): GetBusinessMapResponseDTO {
        ...
    }
}

@Provides
    @Singleton
    fun provideRetrofit() : Retrofit {
        val gsonBuilder = GsonBuilder()
            .registerTypeAdapter(
                GetBusinessMapResponseDTODeserializer::class.java,
                GetBusinessMapResponseDTODeserializer())
            .create()
 
        val retrofit = Retrofit.Builder()
            .baseUrl(IamHereBackendAPI.BASE_URL)
            .addCallAdapterFactory(ResultAdapterFactory())
            .addConverterFactory(GsonConverterFactory.create(gsonBuilder))
            .build()
 
        return retrofit
    }

    @POST("getAllBusinessesByFilterMap")
    suspend fun getBusinessMapByFilter(
        @Body getBusinessMapRequest: GetBusinessMapRequest
    ) : RequestResult<GetBusinessMapResponseDTO>

Hello! Can you please tell me why Gson does not want to use a custom deserializer? I thought the problem was that the response from the api was wrapped in the RequestResult class, but apparently this is not the problem

implementation "com.squareup.retrofit2:retrofit:2.9.0" implementation "com.squareup.retrofit2:converter-gson:2.9.0"

Answer 1

The problem is with your registerTypeAdapter call. The first argument is the class you want to register the adapter for. So instead of providing GetBusinessMapResponseDTODeserializer::class.java you should provide GetBusinessMapResponseDTO::class.java as argument:

val gsonBuilder = GsonBuilder()
    .registerTypeAdapter(
        GetBusinessMapResponseDTO::class.java,
        GetBusinessMapResponseDTODeserializer())
    .create()