Plugin and dependeny:

id 'org.jetbrains.kotlin.plugin.serialization' version "$kotlin_version"
implementation "io.ktor:ktor-serialization:$ktor_version"

Application file:

fun main() {
    embeddedServer(Netty, port = 8080, host = "0.0.0.0") {
        install(ContentNegotiation) {
            json()
        }

        userRouter()
    }.start(wait = true)
}

UserRouter:

fun Application.userRouter() {
    routing {
        get("/users/{id}") {
            val id = call.parameters["id"]?.toInt() ?: -1
            val user = User("Sam", "[email protected]", "abc123")

            val response = if (id == 1) {
                Response("hahaha", false)
            } else {
                Response(user, true)        //< - here, use String type will work
            }

            call.respond(response)
        }
    }
}

User:

@Serializable
data class User(
    val name: String,
    val email: String,
    val password: String
)

Response:

@Serializable
data class Response<T>(
    val data: T,
    val success: Boolean
)

Logs:

2021-12-02 18:04:34.214 [eventLoopGroupProxy-4-1] ERROR ktor.application - Unhandled: GET - /users/7
kotlinx.serialization.SerializationException: Serializer for class 'Response' is not found.
Mark the class as @Serializable or provide the serializer explicitly.
    at kotlinx.serialization.internal.Platform_commonKt.serializerNotRegistered(Platform.common.kt:91)
    at kotlinx.serialization.SerializersKt__SerializersKt.serializer(Serializers.kt:155)

Any help would be appreciated.

CodePudding user response：

The problem is that type for the response variable is Response<out Any> (the lowest common denominator between String and User types is Any) and the serialization framework cannot serialize the Any type.

CodePudding user response：

That's werid, the following works, but to me they are just the same:

get("/users/{id}") {
    val id = call.parameters["id"]?.toInt() ?: -1
    val user = User("Sam", "[email protected]", "abc123")

   /* val response = if (id == 1) {      //<- determine response here won't work, why?
        Response("hahaha", false)
    } else {
        Response(user, true)
    }

    call.respond(response)*/

    if (id == 1) {
        call.respond(Response("hahaha", false))
    } else {
        call.respond(Response(user, true))
    }
}