Gson interface adapter for "Register an InstanceCreator with Gson for this type may fix this problem"

ConfigGson.kt

object ConfigGson {
    fun getGson() = GsonBuilder().apply {
        registerTypeAdapter(Launchable::class.java, InterfaceAdapter<Launchable>())
        registerTypeAdapter(Trigger::class.java, InterfaceAdapter<Trigger>())
    }.create()
}

InterfaceAdapter.kt

import com.google.gson.*
import java.lang.reflect.Type

class InterfaceAdapter<T> : JsonSerializer<T>, JsonDeserializer<T> {

    @Throws(JsonParseException::class)
    override fun deserialize(jsonElement: JsonElement, type: Type,
                             jsonDeserializationContext: JsonDeserializationContext): T {

        val jsonObject = jsonElement.asJsonObject
        val prim = jsonObject.get(CLASSNAME) as JsonPrimitive
        val className = prim.asString
        val klass = getObjectClass(className)
        return jsonDeserializationContext.deserialize(jsonObject.get(DATA), klass)
    }

    override fun serialize(src: T, type: Type?, jsonSerializationContext: JsonSerializationContext?): JsonElement {
        val jsonObject = JsonObject()
        val name: String = (src ?: Any())::class.java.name
        jsonObject.addProperty(CLASSNAME, name)
        jsonObject.add(DATA, jsonSerializationContext?.serialize(src))
        return jsonObject
    }

    /****** Helper method to get the className of the object to be deserialized  */
    fun getObjectClass(className: String): Class<*> {
        try {
            return Class.forName(className)
        } catch (e: ClassNotFoundException) {
            throw JsonParseException(e.message)
        }
    }

    companion object {
        private val CLASSNAME = "CLASSNAME"
        private val DATA = "DATA"
    }

}

Usage.kt

val string = ConfigGson.getGson().toJson(configData)

val configData = ConfigGson.getGson().fromJson(json, ConfigData::class.java)