Custom Adapter for setting default value for enums insude API response.

EnumJsonAdapter.kt

import com.google.gson.JsonDeserializationContext
import com.google.gson.JsonDeserializer
import com.google.gson.JsonElement
import com.google.gson.annotations.SerializedName
import java.lang.reflect.Type

class EnumJsonAdapter<T : Enum<T>>(private val defaultValue: Enum<T>) : JsonDeserializer<Enum<T>> {
    override fun deserialize(
        json: JsonElement?,
        typeOfT: Type?,
        context: JsonDeserializationContext?,
    ): Enum<T> {
        return try {
            if (typeOfT is Class<*> && typeOfT.isEnum) {
                val clazz = typeOfT as? Class<Enum<T>?>

                val value = getValue(clazz, json?.asString)

                val valueOf = java.lang.Enum.valueOf(typeOfT as? Class<Enum<T>?>, value)
                return valueOf
                    ?: defaultValue
            } else {
                defaultValue
            }
        } catch (e: Exception) {
            e.printStackTrace()
            return defaultValue
        }
    }

    fun getValue(clazz: Class<*>?, json: String?): String? {
        val declaredFields = clazz?.declaredFields

        declaredFields?.forEach {
            val annotation = it.getAnnotation(SerializedName::class.java)
            if (annotation?.value != null && annotation.value == json) {
                return it.name
            }
        }
        return json
    }
}

Usage while building retrofit instance.

private val retrofit = Retrofit.Builder() .baseUrl(BuildConfig.API_BASE_URL) .addConverterFactory(GsonConverterFactory.create( GsonBuilder().registerTypeAdapter( OfferType::class.java, EnumJsonAdapter(OfferType.INVALID) ) )) .client(okHttpBuilder.build()) .build()