注册java.util.List时键入适配器警告

Question

尝试注册类型适配器时，其中list为java.util.list

GsonBuilder().registerTypeAdapter(object : TypeToken<List<MyObject>>() {}.type, MyObjectsTypeAdapter())

我收到以下警告：

这个类不应该在Kotlin中使用。使用kotlin.collections.List或kotlin.collections

我的类型适配器使用kotlin.collections.list.

class MyObjectsTypeAdapter: TypeAdapter<List<MyObject>>() {
... 
}

但是，如果我在类型适配器中不使用java.util.List，gson就不能正确匹配类型。

注册类型适配器时，我是否做错了其他事情？

Answer 1

下面是一个小演示，展示了Gson的改装用法。几个要点：

• 要使用Gson作为转换器，您必须添加com.squareup.retrofit2:converter-gson依赖项，并使用addConverterFactory(GsonConverterFactory.create())添加转换器工厂；请参阅改装文档
• 不需要下面示例中的自定义TypeAdapterFactory；它只是展示了如何自定义Gson实例

import com.google.gson.*
import com.google.gson.reflect.TypeToken
import com.google.gson.stream.*
import io.ktor.server.application.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
import io.ktor.server.response.*
import io.ktor.server.routing.*
import retrofit2.*
import retrofit2.converter.gson.GsonConverterFactory
import retrofit2.http.GET
data class MyObject(
val message: String
)
interface DemoService {
@GET("demo")
fun demo(): Call<List<MyObject>>
}
fun main() {
val port = 8080
// Start a demo server returning the JSON response
embeddedServer(Netty, port) {
routing {
get("/demo") {
call.respondText("[{"message":"Hello from server"}]")
}
}
}.start(wait = false)
val gson = GsonBuilder()
.registerTypeAdapterFactory(object: TypeAdapterFactory {
override fun <T> create(gson: Gson, type: TypeToken<T>): TypeAdapter<T>? {
if (type.rawType != MyObject::class.java) {
return null
}
@Suppress("UNCHECKED_CAST") // safe due to type check at beginning
val delegate = gson.getDelegateAdapter(this, type) as TypeAdapter<MyObject>
val adapter = object: TypeAdapter<MyObject>() {
override fun write(writer: JsonWriter, value: MyObject?) {
return delegate.write(writer, value)
}
override fun read(reader: JsonReader): MyObject? {
val value: MyObject? = delegate.read(reader)
return value?.copy(message = "custom-prefix: ${value.message}")
}
}
@Suppress("UNCHECKED_CAST") // safe due to type check at beginning
return adapter as TypeAdapter<T>
}
})
.create()
val retrofit = Retrofit.Builder()
.baseUrl("http://localhost:$port/")
.addConverterFactory(GsonConverterFactory.create(gson))
.build()
val service = retrofit.create(DemoService::class.java)
val response = service.demo().execute()
println(response.body())
}

使用了以下依赖项：

// For demo server
implementation("org.slf4j:slf4j-simple:2.0.0")
implementation("io.ktor:ktor-server-core:2.1.0")
implementation("io.ktor:ktor-server-netty:2.1.0")
implementation("com.squareup.retrofit2:retrofit:2.9.0")
implementation("com.squareup.retrofit2:converter-gson:2.9.0")
implementation("com.google.code.gson:gson:2.9.1")