com.google.gson.internal.LinkedTreeMap 类不能转换为 Partner 类

Question

import com.google.gson.Gson
import com.google.gson.reflect.TypeToken

fun main() {

    val jsonString: String = """{
        "jsonrpc": "2.0",
        "id": null,
        "result": [
            {
                "id": 1,
                "name": "Lekhnath Rijal"
            },
            {
                "id": 2,
                "name": "Administrator"
            }
        ]
    }"""

    val body1 = Gson().fromJson<RpcResult<List<Partner>>>(jsonString, object: TypeToken<RpcResult<List<Partner>>>(){}.type)

    println(body1.result[0].name) // prints Lekhnath Rijal // - As expected

    val body2 = fromJson<RpcResult<List<Partner>>>(jsonString)
    println(body2.result[0].name) // throws Exception as stated below after this code snippet
}

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

data class RpcResult<T>(
    val jsonrpc: String,
    val id: Int?,
    val result: T
)

data class Partner(
    val id: Int,
    val name: String
)

例外：java.lang.ClassCastException: class com.google.gson.internal.LinkedTreeMap cannot be cast to class RpcResult

在不使用函数的情况下将 json 字符串转换为数据类对象时，它按预期工作，但从辅助函数执行相同的代码不起作用，而是引发上述异常。我在这里缺少什么？

Answer 1

这是由于运行时的类型擦除。在 Kotlin 中，您可以通过使函数内联reified类型来解决此问题：

Change your function from:

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

To:

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

For further reading check this out: https://kotlinlang.org/docs/reference/inline-functions.html