why java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.readbook.chinesepoetry.data.model.Response？

Question

I'm a beginner of kotlin Android developer. I come across this problem and I don't know how to resolve it.

I define a kotlin extension function Observable<T>.toTraditional() in order to keep Rx flow call, but I met an exception.

Here is my code:

class Test {
    @Test
    fun test() {
        val json = "{\"result\":{\"curPage\":1,\"data\":[{\"id\":1,\"name\":\"关雎\",\"dynasty\":\"先秦\",\"poet\":\"佚名\",\"content\":\"钟鼓乐之。\"},{\"id\":1213,\"name\":\"伐檀\",\"dynasty\":\"先秦\",\"poet\":\"佚名\",\"content\":\"钟鼓乐之。\"}],\"pageCount\":388,\"size\":20,\"total\":7756},\"status\":1,\"message\":\"成功\"}"
        Observable.create<Response<RecommendListBean>> {
            val response = getResponse<Response<RecommendListBean>>(json)
            it.onNext(response)
        }.toTraditional().subscribe({},{
            println(it)
        })
    }

    inline fun <reified T> getResponse(json: String): T {
        return fromJson(json)
    }

    inline fun <reified T> Observable<T>.toTraditional(): Observable<T> {
        return map {
            val toJson = Gson().toJson(it)
            // In fact, I convert simplified chinese in json to traditional chinese.
            // Here, I intentionally omit that code to make my problem more clearly.
            val result = fromJson<T>(toJson)
            result
        }
    }

    inline fun <reified T> fromJson(json: String?): T {
        return Gson().fromJson<T>(json, object : TypeToken<T>() {}.type)
    }
}

Also, I need to provide my three beans:

data class Response<T>(
        val message: String,
        @SerializedName(value = "result", alternate = ["data"])
        val result: T,
        val status: Int
)

data class RecommendListBean(
        val curPage: Int,
        val data: List<PoetryBean>,
        val pageCount: Int,
        val size: Int,
        val total: Int
)

data class PoetryBean (
    val content: String,
    val dynasty: String,
    val id: Int,
    val name: String,
    val poet: String
)

After runnint the above code, I get the error:

java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to com.readbook.chinesepoetry.data.model.Response

I have look up this exception on the internet, many say that it's because kotlin generics erase. But, I exam my code, they really have reified keyword.

Answer 1

fun <R :Any> Observable<R>.toTraditional(): Observable<R> {
return map {
    val toJson = Gson().toJson(it)
    // In fact, I convert simplified chinese in json to traditional chinese.
    // Here, I intentionally omit that code to make my problem more clearly.
    val result = Gson().fromJson<R>(toJson,it.javaClass)
    result
  }
}

just get the object's class