I have the following response from a backend:
{
"title": "House",
"translations": {
"es": "Casa",
"fr": "Maison",
"de": "Haus"
}
}
To process it I am using the kotlinx serializer and this is my data class.
#Serializable
data class MyRespons(
val title: String,
val translations: Map<String,String>? = null,
)
The property translations is optional, so in some cases I can just get the title (which is fine). What the problem is, is that there also cases where the backend returns this json:
{
"title": "House",
"translations": ""
}
This throws an error because Kotlin is not converting the empty string to a null map but tries to get the properties from it. Is there a way to make Kotlin treat an empty string as if the property was not set at all? (I am trying to not make a custom serializer for this, especially because the map serializer has lots of code...)
Sadly I can't change this backend behavior and have to live with it.
you can wrap Map Serializer with:
object MapSerializer: KSerializer<Map<String,String>> {
override val descriptor: SerialDescriptor
get() = TODO("Not yet implemented")
override fun deserialize(decoder: Decoder): Map<String, String> {
if (decoder.decodeString().isEmpty())
return mapOf()
else
return MapSerializer(String.serializer(),String.serializer()).deserialize(decoder)
}
}
Related
I have a custom implementation of a JsonDeserializer which implements a ContextualDeserializer in order to deserialize a generic class. Everything works fine until the generic class itself has a property which is also a generic class.
For demo purposes, I simplified the code to the minimum
My class is
data class MyObject<out Content>(
val content: Content
)
Deserializing MyObject<String> works:
{
"content": "Hello"
}
but deserializing MyObject<MyObject<String>>> does not:
{
"content": {
"content": "Hello"
}
}
The custom deserializer is the following. The issue seems to be that contextualType.containedType is returning null.
I believe this issue is in the line
val content = ctxt.readTreeAsValue(contentNode, contentType!!.rawClass)
because the .rawClass does not have any additional information about the generic type. So the content is deserialized as just MyObject instead of MyObject<String>.
class MyObjectDeserializer : JsonDeserializer<MyObject<*>?>(), ContextualDeserializer {
private var contentType: JavaType? = null
override fun createContextual(ctxt: DeserializationContext?, property: BeanProperty?): JsonDeserializer<*> {
contentType = if (property == null)
ctxt!!.contextualType.containedType(0)
else
property.type.containedType(0)
if (contentType != null) {
println("${ctxt!!.contextualType} has contained type $contentType")
} else {
// Here is where the issue occurs
println("${ctxt!!.contextualType} does not have any contained types")
}
return this
}
override fun deserialize(p: JsonParser?, ctxt: DeserializationContext): MyObject<*> {
val codec = p?.codec ?: throw NullPointerException()
val node = codec.readTree<JsonNode>(p)
val contentNode = node.get("content")
val content = ctxt.readTreeAsValue(contentNode, contentType!!.rawClass)
return MyObject(content)
}
}
and I register the deserialzers like so
fun ObjectMapper.registerMyDeserializers(): ObjectMapper {
val module = SimpleModule().also {
it.addDeserializer(MyObject::class.java, MyObjectDeserializer())
}
return this.registerModule(module)
}
The unit test the demonstrates the issue is the follow. The first test works fine, the second fails.
class ResponseParsingTests {
private val objectMapper = jacksonObjectMapper().registerMyDeserializers()
#Test
fun `parses String as content`() {
val json = """
{
"content": "Hello"
}
""".trimIndent()
val result = objectMapper.readValue<MyObject<String>>(json)
assertEquals("Hello", result.content)
}
#Test
fun `parses MyObject as content`() {
val json = """
{
"content": {
"content": "Hello"
}
}
""".trimIndent()
val result = objectMapper.readValue<MyObject<MyObject<String>>>(json)
assertEquals("Hello", result.content.content)
}
}
Please note that I'm aware the this example class does not require any custom deserialzer at all. However my real use case is a bit more complex and I need to use a custom deserializer because I'm publishing my code as part of a library which suppoorts multiple serialization frameworks (gson, jackson, kotlinx). So the serialization cannot be part of my actual class but rather in a separate one.
I have some difficulties to deserialise this JSON object from RIOT API:
{
"type":"champion",
"version":"6.1.1",
"data":{
"Thresh":{
"id":412,
"key":"Thresh",
"name":"Thresh",
"title":"the Chain Warden"
},
"Aatrox":{
"id":266,
"key":"Aatrox",
"name":"Aatrox",
"title":"the Darkin Blade"
},...
}
}
Inside the data object we have an other object with fields of all champions.
To not create all champions objects, I want de deserialise this to an list of Champion object, I expect something like that:
{
"type":"champion",
"version":"6.1.1",
"data":[
{
"id":412,
"key":"Thresh",
"name":"Thresh",
"title":"the Chain Warden"
},
{
"id":266,
"key":"Aatrox",
"name":"Aatrox",
"title":"the Darkin Blade"
},...
]
}
I think I have to create a custom Serializer that extends KSerialize but I didn't really know how to do it, can someone help me ?
On C# stackoverflow response is : Deserialize JSON from Riot API C#
There is my solution:
(If someone know witch descriptor to put there I'm interested)
object ChampionsSerializer : KSerializer<List<NetworkChampion>> {
// TODO : Not the good descriptor, fix me
override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("data", kind = PrimitiveKind.STRING)
override fun deserialize(decoder: Decoder): List<NetworkChampion> {
val jsonInput = decoder as? JsonDecoder ?: error("Can be deserialized only by JSON")
val fieldsAsJson = jsonInput.decodeJsonElement().jsonObject
val jsonParser = jsonInput.json
return fieldsAsJson.map {
jsonParser.decodeFromJsonElement(it.value)
}
}
override fun serialize(encoder: Encoder, value: List<NetworkChampion>) {
}
}
#Serializable
data class NetworkChampionsResponse(
val type: String,
val format: String,
val version: String,
#Serializable(ChampionsSerializer::class)
val data: List<NetworkChampion>
)
Json link:
https://ddragon.leagueoflegends.com/cdn/13.1.1/data/fr_FR/champion.json
This question already has an answer here:
kotlinx deserialization: different types && scalar && arrays
(1 answer)
Closed 7 months ago.
With a structure similar to the following:
#Serializable
sealed class Parameters
#Serializable
data class StringContainer(val value: String): Parameters()
#Serializable
data class IntContainer(val value: Int): Parameters()
#Serializable
data class MapContainer(val value: Map<String, Parameters>): Parameters()
// more such as list, bool and other fairly (in the context) straight forward types
And the following container class:
#Serializable
data class PluginConfiguration(
// other value
val parameters: Parameters.MapContainer,
)
I want to reach a (de)serialization where the paramters are configured as a flexible json (or other) map, as one would usually expect:
{
"parameters": {
"key1": "String value",
"key2": 12,
"key3": {}
}
}
And so on. Effectively creating a flexible structure that is still structured enough to not be completely uncontrolled as Any would be. There's a fairly clearly defined (de)serialization, but I cannot figure how to do this.
I've tried reading the following
https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serialization-guide.md
And I do have a hunch that a polymorphic serializer is needed, but so far I'm bumping in to either generic structures, which I believe is way overkill for my purpose or that it for some reason cannot find the serializer for my subclasses, when writing a custom serializer for Parameters.
Update
So using custom serializers combined with surrogate classes, most things are working. The current problem is when values are put into the map, I get a kotlin.IllegalStateException: Primitives cannot be serialized polymorphically with 'type' parameter. You can use 'JsonBuilder.useArrayPolymorphism' instead. Even when I enable array polymorphism this error arises
The answer with kotlinx deserialization: different types && scalar && arrays is basically the answer, and the one I will accept. However, for future use, the complete code to my solution is as follows:
Class hierarchy
#kotlinx.serialization.Serializable(with = ParametersSerializer::class)
sealed interface Parameters
#kotlinx.serialization.Serializable(with = IntContainerSerializer::class)
data class IntContainer(
val value: Int
) : Parameters
#kotlinx.serialization.Serializable(with = StringContainerSerializer::class)
data class StringContainer(
val value: String
) : Parameters
#kotlinx.serialization.Serializable(with = MapContainerSerializer::class)
data class MapContainer(
val value: Map<String, Parameters>
) : Parameters
#kotlinx.serialization.Serializable
data class PluginConfiguration(
val plugin: String,
val parameters: MenuRunnerTest.MapContainer
)
Serializers:
abstract class BaseParametersSerializer<T : Parameters> : KSerializer<T> {
override val descriptor: SerialDescriptor = JsonElement.serializer().descriptor
override fun serialize(encoder: Encoder, value: T) {
fun toJsonElement(value: Parameters): JsonElement = when (value) {
is IntContainer -> JsonPrimitive(value.value)
is MapContainer -> JsonObject(
value.value.mapValues { toJsonElement(it.value) }
)
is StringContainer -> JsonPrimitive(value.value)
}
val sur = toJsonElement(value)
encoder.encodeSerializableValue(JsonElement.serializer(), sur)
}
override fun deserialize(decoder: Decoder): T {
with(decoder as JsonDecoder) {
val jsonElement = decodeJsonElement()
return deserializeJson(jsonElement)
}
}
abstract fun deserializeJson(jsonElement: JsonElement): T
}
object ParametersSerializer : BaseParametersSerializer<Parameters>() {
override fun deserializeJson(jsonElement: JsonElement): Parameters {
return when(jsonElement) {
is JsonPrimitive -> when {
jsonElement.isString -> StringContainerSerializer.deserializeJson(jsonElement)
else -> IntContainerSerializer.deserializeJson(jsonElement)
}
is JsonObject -> MapContainerSerializer.deserializeJson(jsonElement)
else -> throw IllegalArgumentException("Only ints, strings and strings are allowed here")
}
}
}
object StringContainerSerializer : BaseParametersSerializer<StringContainer>() {
override fun deserializeJson(jsonElement: JsonElement): StringContainer {
return when(jsonElement) {
is JsonPrimitive -> StringContainer(jsonElement.content)
else -> throw IllegalArgumentException("Only strings are allowed here")
}
}
}
object IntContainerSerializer : BaseParametersSerializer<IntContainer>() {
override fun deserializeJson(jsonElement: JsonElement): IntContainer {
return when (jsonElement) {
is JsonPrimitive -> IntContainer(jsonElement.int)
else -> throw IllegalArgumentException("Only ints are allowed here")
}
}
}
object MapContainerSerializer : BaseParametersSerializer<MapContainer>() {
override fun deserializeJson(jsonElement: JsonElement): MapContainer {
return when (jsonElement) {
is JsonObject -> MapContainer(jsonElement.mapValues { ParametersSerializer.deserializeJson(it.value) })
else -> throw IllegalArgumentException("Only maps are allowed here")
}
}
}
This structure should be expandable for lists, doubles and other structures, not included in the example :)
I'm trying to build a class where certain values are Observable but also Serializable.
This obviously works and the serialization works, but it's very boilerplate-heavy having to add a setter for every single field and manually having to call change(...) inside each setter:
interface Observable {
fun change(message: String) {
println("changing $message")
}
}
#Serializable
class BlahVO : Observable {
var value2: String = ""
set(value) {
field = value
change("value2")
}
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
println(BlahVO().apply { value2 = "test2" })
correctly outputs
changing value2
{"value2":"test2"}
I've tried introducing Delegates:
interface Observable {
fun change(message: String) {
println("changing $message")
}
#Suppress("ClassName")
class default<T>(defaultValue: T) {
private var value: T = defaultValue
operator fun getValue(observable: Observable, property: KProperty<*>): T {
return value
}
operator fun setValue(observable: Observable, property: KProperty<*>, value: T) {
this.value = value
observable.change(property.name)
}
}
}
#Serializable
class BlahVO : Observable {
var value1: String by Observable.default("value1")
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
println(BlahVO().apply { value1 = "test1" }) correctly triggers change detection, but it doesn't serialize:
changing value1
{}
If I go from Observable to ReadWriteProperty,
interface Observable {
fun change(message: String) {
println("changing $message")
}
fun <T> look(defaultValue: T): ReadWriteProperty<Observable, T> {
return OP(defaultValue, this)
}
class OP<T>(defaultValue: T, val observable: Observable) : ObservableProperty<T>(defaultValue) {
override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
super.setValue(thisRef, property, value)
observable.change("blah!")
}
}
}
#Serializable
class BlahVO : Observable {
var value3: String by this.look("value3")
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
the result is the same:
changing blah!
{}
Similarly for Delegates.vetoable
var value4: String by Delegates.vetoable("value4", {
property: KProperty<*>, oldstring: String, newString: String ->
this.change(property.name)
true
})
outputs:
changing value4
{}
Delegates just doesn't seem to work with Kotlin Serialization
What other options are there to observe a property's changes without breaking its serialization that will also work on other platforms (KotlinJS, KotlinJVM, Android, ...)?
Serialization and Deserialization of Kotlin Delegates is not supported by kotlinx.serialization as of now.
There is an open issue #1578 on GitHub regarding this feature.
According to the issue you can create an intermediate data-transfer object, which gets serialized instead of the original object. Also you could write a custom serializer to support the serialization of Kotlin Delegates, which seems to be even more boilerplate, then writing custom getters and setters, as proposed in the question.
Data Transfer Object
By mapping your original object to a simple data transfer object without delegates, you can utilize the default serialization mechanisms.
This also has the nice side effect to cleanse your data model classes from framework specific annotations, such as #Serializable.
class DataModel {
var observedProperty: String by Delegates.observable("initial") { property, before, after ->
println("""Hey, I changed "${property.name}" from "$before" to "$after"!""")
}
fun toJson(): String {
return Json.encodeToString(serializer(), this.toDto())
}
}
fun DataModel.toDto() = DataTransferObject(observedProperty)
#Serializable
class DataTransferObject(val observedProperty: String)
fun main() {
val data = DataModel()
println(data.toJson())
data.observedProperty = "changed"
println(data.toJson())
}
This yields the following result:
{"observedProperty":"initial"}
Hey, I changed "observedProperty" from "initial" to "changed"!
{"observedProperty":"changed"}
Custom data type
If changing the data type is an option, you could write a wrapping class which gets (de)serialized transparently. Something along the lines of the following might work.
#Serializable
class ClassWithMonitoredString(val monitoredProperty: MonitoredString) {
fun toJson(): String {
return Json.encodeToString(serializer(), this)
}
}
fun main() {
val monitoredString = obs("obsDefault") { before, after ->
println("""I changed from "$before" to "$after"!""")
}
val data = ClassWithMonitoredString(monitoredString)
println(data.toJson())
data.monitoredProperty.value = "obsChanged"
println(data.toJson())
}
Which yields the following result:
{"monitoredProperty":"obsDefault"}
I changed from "obsDefault" to "obsChanged"!
{"monitoredProperty":"obsChanged"}
You however lose information about which property changed, as you don't have easy access to the field name. Also you have to change your data structures, as mentioned above and might not be desirable or even possible. In addition, this work only for Strings for now, even though one might make it more generic though.
Also, this requires a lot of boilerplate to start with. On the call site however, you just have to wrap the actual value in an call to obs.
I used the following boilerplate to get it to work.
typealias OnChange = (before: String, after: String) -> Unit
#Serializable(with = MonitoredStringSerializer::class)
class MonitoredString(initialValue: String, var onChange: OnChange?) {
var value: String = initialValue
set(value) {
onChange?.invoke(field, value)
field = value
}
}
fun obs(value: String, onChange: OnChange? = null) = MonitoredString(value, onChange)
object MonitoredStringSerializer : KSerializer<MonitoredString> {
override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("MonitoredString", PrimitiveKind.STRING)
override fun serialize(encoder: Encoder, value: MonitoredString) {
encoder.encodeString(value.value)
}
override fun deserialize(decoder: Decoder): MonitoredString {
return MonitoredString(decoder.decodeString(), null)
}
}
I have a Kotlin object that I am trying serialize with Gson. A member that is setup as a delegate does not get serialized. The delegation works if I call it directly, as does the onChange callback, but Gson just ignores it.
Is there any way to get Gson to serialize this without writing a custom serializer?
Here is a simplified example of what I'm trying to do:
class MyDelegate() {
fun getProperty(): String {
return "myDelegate Property"
}
fun observableDelegate(onChange: () -> Unit): ReadWriteProperty<Any?, String> {
return object: ReadWriteProperty<Any?, String> {
override fun getValue(thisRef: Any?, property: KProperty<*>): String {
return getProperty()
}
override fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
TODO("not implemented")
}
}
}
}
class MyTest(delegate: MyDelegate, val property0: String = "property0" ) {
val property1 = "property1"
var property2 = "property2"
var property3: String by delegate.observableDelegate {
// onChange called
}
}
Testing it with:
#Test
fun testDelegate() {
val t1 = MyTest(MyDelegate())
val s1 = Gson().toJson(t1)
Assert.fail(s1)
}
Output:
{"property1":"property1","property2":"property2","property0":"property0"}
The property3 variable is not field backed. Thus Gson doesn't consider it as field in the Json serialization.
The GsonDesignDocument states for properties as such
Some Json libraries use the getters of a type to deduce the Json elements. We chose to use all fields (up the inheritance hierarchy) that are not transient, static, or synthetic. We did this because not all classes are written with suitably named getters. Moreover, getXXX or isXXX might be semantic rather than indicating properties.
So you might have to implement a custom (de)serializer for your needs.