java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to X error when call to X error when call Gson fromJson for generic type

Question

Hi I have this code in Kotlin Android I try to parse JSON string to data clas, but the data is unknown, I mean the data class is genric type T

class JsonFeatureFlag<T>(
        key: String,
        @StringRes nameResId: Int,
        category: DevOptionCategory,
        val defaultValue: T
    ): FeatureFlagV2<T>(key, nameResId, category) {
    .....
    override fun getValue(): T {
            val json = FirebaseRemoteConfig.getInstance().getString(key)
            return try {
                Gson().fromJson(json, object: TypeToken<T>(){}.type)
            } catch (e: Exception) {
                reportInvalidJson(json)
                defaultValue
            }
        }
    ....
    }

And I'm getting this error: java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to X

While I understand that TypeToken should be used for generic, something isn't working.

Answer 1

To solve this problem I provide a class name ie className: Class Although I used genric, when somebody wants to use my API and call getValue the type is known, and he can provide the class name to the get value method.

class JsonFeatureFlag<T>(
    key: String,
    @StringRes nameResId: Int,
    category: DevOptionCategory,
    val defaultValue: T
): FeatureFlagV2<T>(key, nameResId, category) {


     fun getValue(className: Class<T>): T {
        val json = FirebaseRemoteConfig.getInstance().getString(key)
        return try {
            Gson().fromJson(json, className)
        } catch (e: Exception) {
            reportInvalidJson(json)
            defaultValue
        }
    }