Hello, I have a class (external, can't edit source), that I made a custom serializer for. It works fine like this:

@Serializable(with = MySerializer::class) val item: MyClass

But now I need to serialize a list of these items:

val items: List<MyClass>

How can I make it work? I cannot use the same annotation, since now it's a

List

.

Another question: I need to deserialize an object with a property that can either be a boolean or a nested object. How can I achieve this with kotlinx.serialization?

In a new IntelliJ kotlin multiplatform project after adding

kotlin("plugin.serialization")

and serialization dependency in common module I don't get generated serializers and get a warning on

@Serializable

kotlinx.serialization compiler plugin is not applied to the module, so this annotation would not be processed. Make sure that you've setup your buildscript correctly and re-import project.

The main build.gradle.kts contains proper buildscript dependencies

classpath(kotlin("gradle-plugin", version = "1.4.31"))
classpath(kotlin("plugin.serialization", version = "1.4.31"))

Nothing seems to help. I've removed all unnecessary code, reimported project, invalidated caches but to no avail. Any ideas?

Is there an "idiomatic" way to assign the default value of a property when a

JsonDecodingException

is produced BECAUSE of that property? I can workaround it by using a custom serializer for that property but it's quite an overhead. e.g - for this data class

data class AA(val a: Int = 0)

and this json

{"a":"N/A"}

I will get this output

AA(a = 0)

despite it failed to decode it.

Hi! :android-wave: This might be a dumb question, but is it possible to annotate and auto-generate serializers for a POJO class in a java file? I am trying something like this

// MainActivity.java

public class MainActivity extends Activity {

    @Serializable
    static class Props {
        // my POJO
        int count;
        String name;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Props.serializer() // No such method available
    }
}

I am not sure if i am misusing / misunderstanding the API here, so feel free to correct 🙂 Thx!

Hi, I am trying to serialize data class and getting empty object as result, I can't find out what is wrong

@Serializable
data class Params(val deviceId: String = "someId")

val params = Params()

val result  = Json.encodeToString(Params.serializer(), params)
console.log("params", params)
console.log("result ",  result)

I get this result:

Hi, I am getting an error and I can't figure out how the default polymorphic serializer is messing it up:

kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 26: Expected '[, kind: SEALED'

Any help is appreciated.

Is the JSON serializer deterministic? i.e. if two input data classes are equal, will it always produce the same output, regardless of where and when? I think we can assume the same version of kotlinx-serialization is always used.

hello 🙂. is there something similar to

@JsonAnyGetter

from jackson in kotlinx serialization? or, assuming I have a json like

{
  field: value,
  second: value,
  another: value
}

how can I map into something a class like

@Serializable
class MyClass(val field: String, val additional: Map<String, String>)

? bonus question, coming from jackson, I spent most of day trying to figure out how to handle

val additional: Map<String, Any>

, but that is not really possible with kotlin serialization right?

Hi can anyone help we with kotlin deserialization? I’m using retrofit with kotlinx serialization and I have a case where I can get 2 types of responses from the server: the first case returns a list of results with “drinks” key,

{"drinks":[{"strDrink":"Jelly Bean","strDrinkThumb":"https:\/\/<http://www.thecocktaildb.com|www.thecocktaildb.com>\/images\/media\/drink\/bglc6y1504388797.jpg","idDrink":"13775"},{"strDrink":"Turf Cocktail","strDrinkThumb":"https:\/\/<http://www.thecocktaildb.com|www.thecocktaildb.com>\/images\/media\/drink\/utypqq1441554367.jpg","idDrink":"12418"}]}

but sometimes the server returns the following:

"{"drinks":"None Found"}"

Before using kotlinx I had a custom type convertor with Gson, and that worked fine, but I’m struggling with kotlin. I tried to create a KSerializer to try to parse the result, and return an object with an empty list if an exception is thrown, but I keep getting this exception:

java.lang.IllegalStateException: Reader has not consumed the whole input: JsonReader(source='{"drinks":"None Found"}', currentPosition=22, tokenClass=1, tokenPosition=10, offset=11)

Any ideas how to solve this? I can always return a string instead of a data class, but this is ugly AF

I see that protobuf for kotlinx.serialization is still considered “experimental”. In what regard is it experimental? Are certain features in JSON not supported in protobuf?

Hi all! I’m having an annoying problem with Proguard for Kotlinx Serialization. I have a class like this

@Serializable
data class PagedResult<T, P : PagedResult.Pagination>(val items: List<T>, val pagination: P)

Everything works fine until the moment when I enable Proguard. An error like this occurs: java.lang.IllegalArgumentException: Unable to create converter for f.a.b.d.i.g.a<> (). f.a.b.d.i.g.a is just a class PagedResult (I see it in mapping.txt) The rules for Proguard are taken from the official kotlinx.serialization repository. Can someone tell me what the problem is?

Given a class like

data class Foo(val foo: String)

is there an easy way to serialize it into just a string, not an object like

{"foo": "SomeString"}

? without writing a custom serializer...

Huh, switching kotlinx.serialization to 1.2.0 (unreleased?) seems to fix it...

Hi, I’m testing my model w/ json serialization. I’m serializing my models to json and then deserializing them back into my model object. Nodejs and native mac are working fine, but the test on java is throwing this cryptic error

java.lang.ClassCastException: class [[Ljava.lang.Object; cannot be cast to class [[Ljava.lang.Float; ([[Ljava.lang.Object; and [[Ljava.lang.Float; are in module java.base of loader 'bootstrap')
	at raytracer.math.Matrix$$serializer.deserialize(Matrix.kt:9)
	at raytracer.math.Matrix$$serializer.deserialize(Matrix.kt:9)
	at kotlinx.serialization.json.internal.PolymorphicKt.decodeSerializableValuePolymorphic(Polymorphic.kt:63)
	at kotlinx.serialization.json.internal.StreamingJsonDecoder.decodeSerializableValue(StreamingJsonDecoder.kt:32)
	at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableValue(AbstractDecoder.kt:43)
	at kotlinx.serialization.encoding.AbstractDecoder.decodeSerializableElement(AbstractDecoder.kt:70)

Any ideas of where to look and how to fix that?

I have upgraded to 1.5.0-RC and I get this error no matter what I try :( Stacktrace:

'void kotlinx.serialization.modules.SerialModuleImpl.<init>(java.util.Map, java.util.Map, java.util.Map, java.util.Map)'

java.lang.NoSuchMethodError: 'void kotlinx.serialization.modules.SerialModuleImpl.<init>(java.util.Map, java.util.Map, java.util.Map, java.util.Map)'

at kotlinx.serialization.modules.SerializersModuleKt.<clinit>(SerializersModule.kt:74)

at kotlinx.serialization.json.Json$Default.<init>(Json.kt:65)

at kotlinx.serialization.json.Json$Default.<init>(Json.kt)

at kotlinx.serialization.json.Json.<clinit>(Json.kt)

at kotlinx.serialization.json.JsonKt.Json$default(Json.kt:130)

- Kotlin version: 1.5.0

- kotlinx-serialization version: 1.2.0

- Kotlin platforms: multiplatform (JVM + JS)

- Gradle version: 6.8.3

- IDE version: 2021.1.1 RC

- Other relevant context: Java 15

Have you seen anything similar? Thanks.

hey all, I'm having some trouble with dynamic deserialization on kotlin native. i've included relevant code in the thread. would appreciate some help on this one, thank you in advance!

Hi folks! I have an error in generic class after upgrade serialization to 1.2.0. Can you suggest why?

hi, how can I make data class with empty arrays encode to empty json arrays?

val jsonMapper = Json {
        prettyPrint = true
        encodeDefaults = true
        coerceInputValues = true
      }
      val inputPet = Pet(
        name = petName,
        tags = emptyList(),
        photoUrls = emptyList(),
        status = petStatus
      )
      val inputPetJson = jsonMapper.encodeToString(inputPet)

Actual :{"name":"blaaaah","status":"available"}
Expected:{"name":"blaaaah","photoUrls":[],"tags":[],"status":"available"}

I’ve tried various combinations of encodeDefaults and coerceInputValues. The problem is that

Pet

has other fields that default to null. I don’t want to include those.

Hello. I bumped into issue: serialization works well in JVM, but fails in JS with exception (

1.2.0

library version):

TypeError: tmp$.serializer is not a function
	at <global>.compiledSerializerImpl(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:72080)
	at <global>.serializerOrNull(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:67234)
	at <global>.reflectiveOrContextual(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:67226)
	at <global>.builtinSerializer(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:67220)
	at <global>.serializerByKTypeImpl(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:67159)
	at <global>.serializer(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:67129)
	at data.OperationResultSerializationTest.operationSuccessSerializationTest(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:77540)
	at <global>.<unknown>(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:77588)
	at Context.<anonymous>(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_490920/commons.js:57)

Or (with

1.1.0

library version):

SerializationException: Serializer for class 'OperationResult' is not found.
Mark the class as @Serializable or provide the serializer explicitly.
On Kotlin/JS explicitly declared serializer should be used for interfaces and enums without @Serializable annotation
	at Object.captureStack(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:40068)
	at SerializationException.constructor(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:40401)
	at SerializationException.constructor(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:40427)
	at SerializationException.constructor(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:40447)
	at IllegalArgumentException.init(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:40458)
	at SerializationException.init(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:67048)
	at <global>.platformSpecificSerializerNotRegistered(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:72030)
	at <global>.serializer(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:67125)
	at data.OperationResultSerializationTest.operationSuccessSerializationTest(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:77226)
	at <global>.<unknown>(C:/Users/Akela/AppData/Local/Temp/_karma_webpack_73575/commons.js:77274)

I described the issue: https://github.com/Kotlin/kotlinx.serialization/issues/1448 Could you help me? Is there a workaround?

Updated a big KMP multi-module project to Kotlin 1.5.0 and kotlinx.serialization 1.2.0 and I get this error while building a very small module with just 3 files. Is there a way to know what causes this?

How are custom formats types supposed to be handled/represented? SerialInfo annotation? inline class? Custom serializer for annotation?

This bug https://github.com/Kotlin/kotlinx.serialization/issues/1464 makes 1.2.0 release completely unusable in realworld apps. Can we expect a quick hotfix release?

Hello everyone, 👋🏽 I’ve had a look at Kotlinx.Serialization documentation, and also looked for examples, but I couldn’t find the best practice for the case I’m going to describe. I wonder if anyone would be able to provide any insight. Also, I’m not an advanced user of the library. I have an server that return a JSON Payload containing a single Status property:

{
  "status": "OneOf<Pending|Queued|InProgress|Finished|NotBuilt>"
}

If I want to serialise it to Enum, I would have:

@Serializable
enum class Status {
    @SerialName("Pending") PENDING,
    @SerialName("Queued") QUEUED,
    @SerialName("InProgress") IN_PROGRESS,
    @SerialName("Finished") FINISHED,
    @SerialName("NotBuilt") NOT_BUILT,
}

@Serializable
data class ServerResponseModel(val status: Status)

However, when I get a response from the server, let’s say

InProgress

all I need to do is build a new Model and return the status as being

IN_PROGRESS

. What would be the best way to achieve that? Do I need to write a custom serialisation in this case? Also, does it makes sense to create an

Enum class

for

ServerResponseModel

? Thanks for your assistance.

Trying serialization 1.2.0 in existing MPP lib, using Kotlin compiler 1.4.32. I get the following on iOS (when parsing a JSON network response):

kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen kotlin.collections.HashMap@955628

This works fine with serialization 1.1.0. Should the new serialization work with Kotlin 1.4.32? Do we need an updated coroutines lib?

When using polymorphic serialization is there any way to 1. have the class discriminator available as a property on the base class 2. default to a particular subclass? My usecase has the

type

property on the json object somewhat overloaded where for one value i want to deserialize it into class A, but any other value is of type B and I need access to the

type

value. Adding

type

as a property gives an error

because it has property name that conflicts with JSON class discriminator 'type'. You can either change class discriminator in JsonConfiguration, rename property with @SerialName annotation or fall back to array polymorphism

I couldnt find any reference too array polymorphism anywhere

Found completely random bug

@Serializable
data class Example(val content: String)

suspend fun main(args: Array<String>) {
    val content2 = "a".repeat(126) + "\n"
    Json.encodeToString(content2)
}

This fails if as long as the number is >= 126

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 129 out of bounds for length 129
	at kotlinx.serialization.json.internal.JsonStringBuilder.appendStringSlowPath(JsonStringBuilder.kt:102)
	at kotlinx.serialization.json.internal.JsonStringBuilder.appendQuoted(JsonStringBuilder.kt:61)
	at kotlinx.serialization.json.internal.Composer.printQuoted(Composers.kt:42)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeString(StreamingJsonEncoder.kt:203)
	at kotlinx.serialization.internal.StringSerializer.serialize(Primitives.kt:139)
	at kotlinx.serialization.internal.StringSerializer.serialize(Primitives.kt:136)
	at kotlinx.serialization.json.internal.StreamingJsonEncoder.encodeSerializableValue(StreamingJsonEncoder.kt:211)
	at kotlinx.serialization.json.Json.encodeToString(Json.kt:80)

Is there a way to user kotlinx serialization in a foo.main.kts?