Kotlinx Serialization, avoid crashes on other datatype

Question

I'm using external API in the app, while deserialisation is done with Kotlinx Serialization package, i'm facing issues when api result is Array of Int for multiple values and primitive int for single value. How can i avoid crash in this process. Is there better approach to avoid crashes or creating data classes

ex:

import kotlinx.serialization.Serializable

@Serializable

data class Bookings (val slots: List<Int>)

when slots is having single value API returns {slots: 1} when slots is having multiple value API return { slots: [1,2,3,4]}

score 4 · Accepted Answer · answered Oct 04 '19 at 06:04

It can be done with custom serializer:

import kotlinx.serialization.*
import kotlinx.serialization.json.Json
import kotlinx.serialization.json.JsonInput
import kotlinx.serialization.json.JsonObject
import kotlinx.serialization.json.int

@Serializable(with = BookingsSerializer::class)
data class Bookings(val slots: List<Int>)

@Serializer(forClass = Bookings::class)
object BookingsSerializer : KSerializer<Bookings> {
    override fun deserialize(decoder: Decoder): Bookings {
        val json = (decoder as JsonInput).decodeJson().jsonObject
        return Bookings(parseSlots(json))
    }

    private fun parseSlots(json: JsonObject): List<Int> {
        val slotsJson = json["slots"] ?: return emptyList()
        return try {
            slotsJson.jsonArray.content.map { it.int }
        } catch (e: Exception) {
            listOf(slotsJson.int)
        }
    }
}

@ImplicitReflectionSerializer
fun main() {
    val json = """{"slots": 1}"""
    val result = Json.parse<Bookings>(json)
    println(result) // prints Bookings(slots=[1])
}

Is there way other than custom serializer – OK200 Oct 04 '19 at 06:09 — OK200, Oct 04 '19 at 06:09
at least I don't know about them :) – Andrei Tanana Oct 04 '19 at 07:20 — Andrei Tanana, Oct 04 '19 at 07:20
Class names seem to be outdated – xjcl Jul 01 '21 at 10:08 — xjcl, Jul 01 '21 at 10:08

score 2 · Answer 2 · answered Jul 01 '21 at 10:39

I updated @Andrei's answer for 2021 since the class and method names have changed a bit since 2019:

import kotlinx.serialization.*
import kotlinx.serialization.json.*
import kotlinx.serialization.encoding.Decoder

@Serializable(with = BookingsSerializer::class)
data class Bookings(val slots: List<Int>)

@Serializer(forClass = Bookings::class)
object BookingsSerializer : KSerializer<Bookings> {
    override fun deserialize(decoder: Decoder): Bookings {
        val json = (decoder as JsonDecoder).decodeJsonElement().jsonObject
        return Bookings(parseSlots(json))
    }

    private fun parseSlots(json: JsonObject): List<Int> {
        val slotsJson = json["slots"] ?: return emptyList()
        return try {
            slotsJson.jsonArray.map { it.jsonPrimitive.int }
        } catch (e: Exception) {
            listOf(slotsJson.jsonPrimitive.int)
        }
    }
}

val json = """{"slots": 1}"""
val result = Json.decodeFromString<Bookings>(json)
println(result.toString()) // prints Bookings(slots=[1])

Kotlinx Serialization, avoid crashes on other datatype

2 Answers2

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