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", "sam#gmail.com", "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.
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.
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", "sam#gmail.com", "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))
}
}
You should give a type to a generic when you set a nullable generic to null, otherwise, the plugin doesn't know how to serialize it.
for eg.
//define
#Serializable
data class Response<T>(
val data: T?,
val success: Boolean
)
///usage:
val response = Response<String>(null, false)
Related
When implementing a REST API with Ktor (and Kotlin), it supports the optional field handling of Kotlin. Which works for POST and GET, but what about PATCH (update)?
For example, you have the following resource:
#Serializable
data class MyAddress(
var line1: String? = null,
var line2: String? = null,
var city: String? = null,
var postal_code: String? = null,
var state: String? = null,
var country: String? = null
)
So all MyAddress fields are optional (with a default value).
When you create an address with POST:
"line1" : "line1",
"country" : "XX"
and you than want to remove the country with a PATCH:
"country" : null
the end result of the resource should be:
"line1" : "line1"
But how can you determine this by parsing the json of the PATCH request? Because there is no way, as far as I know, to determine if it was null by default, or submitted.
Furthermore, the default null value for the MyAddress is required, because else the parsing will not work.
Code example:
import kotlinx.serialization.decodeFromString
import kotlinx.serialization.json.Json
#kotlinx.serialization.Serializable
data class MyAddress(
var line1: String? = null,
var line2: String? = null,
var city: String? = null,
var postal_code: String? = null,
var state: String? = null,
var country: String? = null
)
fun main() {
val jsonStringPOST = "{\"line1\":\"street\",\"country\":\"GB\"}"
println("JSON string is: $jsonStringPOST")
val myAddressPost = Json.decodeFromString<MyAddress>(jsonStringPOST)
println("MyAddress object: $myAddressPost")
val jsonStringPATCH = "{\"country\":null}"
println("JSON string is: $jsonStringPATCH")
val myAddressPatch = Json.decodeFromString<MyAddress>(jsonStringPATCH)
println("MyAddress object: $myAddressPatch")
}
I tried to add Optional<String>? as well, but it complains about missing serialization of Optional, and preferably I do not want to make all my data var's Optionals.
Note: I am looking for a more structured solution, that also works with all other resources in the api (10+ classes).
A second solution, based on Aleksei's example:
#Serializable
data class Address2(val line1: OptionalValue<String> = Undefined, val country: OptionalValue<String> = Undefined)
#Serializable(with = OptionalValueSerializer::class)
sealed interface OptionalValue<out T>
object Undefined: OptionalValue<Nothing> {
override fun toString(): String = "Undefined"
}
object Absent: OptionalValue<Nothing> {
override fun toString(): String = "Absent"
}
class WithValue<T>(val value: T): OptionalValue<T> {
override fun toString(): String = value.toString()
}
open class OptionalValueSerializer<T>(private val valueSerializer: KSerializer<T>) : KSerializer<OptionalValue<T>> {
override val descriptor: SerialDescriptor = valueSerializer.descriptor
override fun deserialize(decoder: Decoder): OptionalValue<T> {
return try {
WithValue(valueSerializer.deserialize(decoder))
} catch (cause: SerializationException) {
Absent
}
}
override fun serialize(encoder: Encoder, value: OptionalValue<T>) {
when (value) {
is Undefined -> {}
is Absent -> { encoder.encodeNull() }
is WithValue -> valueSerializer.serialize(encoder, value.value)
}
}
}
fun main() {
val jsonStringPOST = "{\"line1\":\"street\",\"country\":\"GB\"}"
println("JSON string is: $jsonStringPOST")
val myAddressPost = Json.decodeFromString<Address2>(jsonStringPOST)
println("MyAddress object: $myAddressPost")
val jsonStringUPDATE = "{\"country\":null}"
println("JSON string is: $jsonStringUPDATE")
val myAddressUpdate = Json.decodeFromString<Address2>(jsonStringUPDATE)
println("MyAddress object: $myAddressUpdate")
if(myAddressUpdate.country is Absent || myAddressUpdate.country is WithValue) {
println("Update country: ${myAddressUpdate.country}")
} else {
println("No update for country: ${myAddressUpdate.country}")
}
}
Output is:
JSON string is: {"line1":"street","country":"GB"}
MyAddress object: Address2(line1=street, country=GB)
JSON string is: {"country":null}
MyAddress object: Address2(line1=Undefined, country=Absent)
Update country: Absent
You can use a sealed interface for a part of an address to represent undefined value, absence of value, and actual value. For this interface, you need to write a serializer that will encode and decode values accordingly to your logic. I'm not good at the kotlinx.serialization framework so I wrote an example as simple as possible.
import io.ktor.serialization.kotlinx.json.*
import io.ktor.server.application.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
import io.ktor.server.plugins.contentnegotiation.*
import io.ktor.server.request.*
import io.ktor.server.routing.*
import kotlinx.serialization.*
import kotlinx.serialization.descriptors.PrimitiveKind
import kotlinx.serialization.descriptors.PrimitiveSerialDescriptor
import kotlinx.serialization.descriptors.SerialDescriptor
import kotlinx.serialization.encoding.Decoder
import kotlinx.serialization.encoding.Encoder
fun main() {
embeddedServer(Netty, port = 4444) {
install(ContentNegotiation) {
json()
}
routing {
post {
val address = call.receive<Address>()
println(address)
}
}
}.start()
}
#Serializable
data class Address(val line1: MyValue = Undefined, val country: MyValue = Undefined)
#Serializable(with = AddressValueSerializer::class)
sealed interface MyValue
object Undefined: MyValue {
override fun toString(): String = "Undefined"
}
object Absent: MyValue {
override fun toString(): String = "Absent"
}
class WithValue(val value: String): MyValue {
override fun toString(): String = value
}
object AddressValueSerializer: KSerializer<MyValue> {
override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("AddressValue", PrimitiveKind.STRING)
override fun deserialize(decoder: Decoder): MyValue {
return try {
WithValue(decoder.decodeString())
} catch (cause: SerializationException) {
Absent
}
}
#OptIn(ExperimentalSerializationApi::class)
override fun serialize(encoder: Encoder, value: MyValue) {
when (value) {
is Undefined -> {}
is Absent -> { encoder.encodeNull() }
is WithValue -> { encoder.encodeString(value.value) }
}
}
}
With some help from medium.com, I came to the following solution:
#Serializable(with = OptionalPropertySerializer::class)
open class OptionalProperty<out T> {
object NotPresent : OptionalProperty<Nothing>()
data class Present<T>(val value: T) : OptionalProperty<T>() {
override fun toString(): String {
return value.toString()
}
}
fun isPresent() : Boolean {
return this is Present
}
fun isNotPresent(): Boolean {
return this is NotPresent
}
fun isEmpty(): Boolean {
return (this is Present) && this.value == null
}
fun hasValue(): Boolean {
return (this is Present) && this.value != null
}
override fun toString(): String {
if(this is NotPresent) {
return "<NotPresent>"
}
return super.toString()
}
}
open class OptionalPropertySerializer<T>(private val valueSerializer: KSerializer<T>) : KSerializer<OptionalProperty<T>> {
override val descriptor: SerialDescriptor = valueSerializer.descriptor
override fun deserialize(decoder: Decoder): OptionalProperty<T> =
OptionalProperty.Present(valueSerializer.deserialize(decoder))
override fun serialize(encoder: Encoder, value: OptionalProperty<T>) {
when (value) {
is OptionalProperty.NotPresent -> {}
is OptionalProperty.Present -> valueSerializer.serialize(encoder, value.value)
}
}
}
#Serializable
private data class MyAddressNew(
var line1: OptionalProperty<String?> = OptionalProperty.NotPresent,
var line2: OptionalProperty<String?> = OptionalProperty.NotPresent,
var city: OptionalProperty<String?> = OptionalProperty.NotPresent,
var postal_code: OptionalProperty<String?> = OptionalProperty.NotPresent,
var state: OptionalProperty<String?> = OptionalProperty.NotPresent,
var country: OptionalProperty<String?> = OptionalProperty.NotPresent,
)
fun main() {
val jsonStringPOST = "{\"line1\":\"street\",\"country\":\"GB\"}"
println("JSON string is: $jsonStringPOST")
val myAddressPost = Json.decodeFromString<MyAddressNew>(jsonStringPOST)
println("MyAddress object: $myAddressPost")
val jsonStringUPDATE = "{\"country\":null}"
println("JSON string is: $jsonStringUPDATE")
val myAddressUpdate = Json.decodeFromString<MyAddressNew>(jsonStringUPDATE)
println("MyAddress object: $myAddressUpdate")
if(myAddressUpdate.country.isPresent()) {
println("Update country: ${myAddressUpdate.country}")
} else {
println("No update for country: ${myAddressUpdate.country}")
}
}
This prints:
JSON string is: {"line1":"street","country":"GB"}
MyAddress object: MyAddressNew(line1=street, line2=<NotPresent>, city=<NotPresent>, postal_code=<NotPresent>, state=<NotPresent>, country=GB)
JSON string is: {"country":null}
MyAddress object: MyAddressNew(line1=<NotPresent>, line2=<NotPresent>, city=<NotPresent>, postal_code=<NotPresent>, state=<NotPresent>, country=null)
Update country: null
With ktor client, I've got a non-serializable object derived from a serializable object like so:
#Serializable
#SerialName("login-request")
open class LoginRequest (
open val email : String = "",
open val password : String = ""
) : ServiceRequestPayload
impl class
class LoginRequestVo : LoginRequest("", ""), NodeComponent by NodeComponentImpl() {
override val email: String by subject("")
override val password: String by subject("")
}
Now when I manually use kotlinx serialization on this like so:
val request : LoginRequest = LoginRequestVo().apply {
email = "test#gmail.com"
password = "password"
}
val str = Json.encodeToString(request)
println(str)
It correctly serializes it, and when deserialized on the other side, it correctly deserializes to LoginRequest. However, when I use ktor-client to serialize my object, it complains that LoginRequestVo is not serializable. The example code below uses some other objects from my project and has more information that you need, but the gist is that the type of U in the invoke function and therefore the request.payload expression is type LoginRequest as specified by the LoginServiceImpl below.
suspend inline fun <T, U: ServiceRequestPayload> HttpClient.invoke(desc : EndpointDescriptor<T, U>, request : ServiceRequest<U>? ) : ServiceResponse {
val path = "/api${desc.path}"
return when(desc.method) {
HttpMethod.GET -> {
get(path)
}
HttpMethod.POST -> {
if (request == null) {
post(path)
} else {
post(path) {
contentType(ContentType.Application.Json)
body = request.payload
}
}
}
HttpMethod.DELETE -> delete(desc.path)
HttpMethod.PUT -> {
if (request == null) {
put(path)
} else {
post(path) {
contentType(ContentType.Application.Json)
body = request.payload
}
}
}
}
}
class LoginServiceImpl(
context : ApplicationContext
) : LoginService {
private val client by context.service<HttpClient>()
override suspend fun login(request: ServiceRequest<LoginRequest>) = client.invoke(LoginServiceDesc.login, request)
override suspend fun register(request: ServiceRequest<LoginRequest>) = client.invoke(LoginServiceDesc.register, request)
}
The error I get is:
My question is, Is there a way to specify to ktor-client the type or the serializer to use when it needs to serialize a body?
Let's say I'm having a class like:
#Serializable
data class MyClass(
#SerialName("a") val a: String?,
#SerialName("b") val b: String
)
Assume the a is null and b's value is "b value", then Json.stringify(MyClass.serializer(), this) produces:
{ "a": null, "b": "b value" }
Basically if a is null, I wanted to get this:
{ "b": "b value" }
From some research I found this is currently not doable out of the box with Kotlinx Serialization so I was trying to build a custom serializer to explicitly ignore null value. I followed the guide from here but couldn't make a correct one.
Can someone please shed my some light? Thanks.
You can use explicitNulls = false
example:
#OptIn(ExperimentalSerializationApi::class)
val format = Json { explicitNulls = false }
#Serializable
data class Project(
val name: String,
val language: String,
val version: String? = "1.3.0",
val website: String?,
)
fun main() {
val data = Project("kotlinx.serialization", "Kotlin", null, null)
val json = format.encodeToString(data)
println(json) // {"name":"kotlinx.serialization","language":"Kotlin"}
}
https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/json.md#explicit-nulls
Use encodeDefaults = false property in JsonConfiguration and it won't serialize nulls (or other optional values)
Try this (not tested, just based on adapting the example):
#Serializable
data class MyClass(val a: String?, val b: String) {
#Serializer(forClass = MyClass::class)
companion object : KSerializer<MyClass> {
override val descriptor: SerialDescriptor = object : SerialClassDescImpl("MyClass") {
init {
addElement("a")
addElement("b")
}
}
override fun serialize(encoder: Encoder, obj: MyClass) {
encoder.beginStructure(descriptor).run {
obj.a?.let { encodeStringElement(descriptor, 0, obj.a) }
encodeStringElement(descriptor, 1, obj.b)
endStructure(descriptor)
}
}
override fun deserialize(decoder: Decoder): MyClass {
var a: String? = null
var b = ""
decoder.beginStructure(descriptor).run {
loop# while (true) {
when (val i = decodeElementIndex(descriptor)) {
CompositeDecoder.READ_DONE -> break#loop
0 -> a = decodeStringElement(descriptor, i)
1 -> b = decodeStringElement(descriptor, i)
else -> throw SerializationException("Unknown index $i")
}
}
endStructure(descriptor)
}
return MyClass(a, b)
}
}
}
Since I was also struggling with this one let me share with you the solution I found that is per property and does not require to create serializer for the whole class.
class ExcludeIfNullSerializer : KSerializer<String?> {
override fun deserialize(decoder: Decoder): String {
return decoder.decodeString()
}
override val descriptor: SerialDescriptor
get() = PrimitiveSerialDescriptor("ExcludeNullString", PrimitiveKind.STRING)
override fun serialize(encoder: Encoder, value: String?) {
if (value != null) {
encoder.encodeString(value)
}
}
}
will work as expected with the following class
#Serializable
class TestDto(
#SerialName("someString")
val someString: String,
#SerialName("id")
#EncodeDefault(EncodeDefault.Mode.NEVER)
#Serializable(with = ExcludeIfNullSerializer::class)
val id: String? = null
)
Note the #EncodeDefault(EncodeDefault.Mode.NEVER) is crucial here in case you using JsonBuilder with encodeDefaults = true, as in this case the serialization library will still add the 'id' json key even if the value of id field is null unless using this annotation.
JsonConfiguration is deprecated in favor of Json {} builder since kotlinx.serialization 1.0.0-RC according to its changelog.
Now you have to code like this:
val json = Json { encodeDefaults = false }
val body = json.encodeToString(someSerializableObject)
As of now, for anyone seeing this pos today, default values are not serialized (see https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/basic-serialization.md#defaults-are-not-encoded-by-default)
So you simply add to set a default null value, and it will not be serialized.
I am just playing around with vert.x 3.5.3 Kotlin and I am unable to parse a JSON string into a Data class using gson.
Here is the code
class DataVerticle : AbstractVerticle() {
override fun start(startFuture: Future<Void>) {
data class Product(
#SerializedName("id") val id: Int,
#SerializedName("name") val name: String,
#SerializedName("productCode") val productCode: String
)
val products: MutableList<Product> = mutableListOf()
val gson = Gson()
val eventBus = vertx.eventBus()
eventBus.consumer<String>("data.verticle") {
when (it.headers().get("ACTION")) {
"ADD_PRODUCT" -> {
val prodJson = it.body()
if (prodJson != null) {
println(prodJson)
val product = gson.fromJson(prodJson, Product::class.java)
println(product)
it.reply("SUCCESS")
}
}
else -> {
print("ERROR")
}
}
}
startFuture.complete()
}
}
The Problem is the parsed value is always null
Here is my sample json ->
{"id":1,"name":"SOAP","productCode":"P101"}
The json string sent over the eventBus is not null.
I am using this package for gson
com.google.code.gson', version: '2.8.5'
Thanks
You declare your class inside the method body, which Gson doesn't like much.
Extracting it to be nested class will work just fine:
class DataVerticle : AbstractVerticle() {
override fun start(startFuture: Future) {
val gson = Gson()
val eventBus = vertx.eventBus()
eventBus.consumer<String>("data.verticle") {
when (it.headers().get("ACTION")) {
"ADD_PRODUCT" -> {
val prodJson = it.body()
if (prodJson != null) {
println(prodJson)
val product = gson.fromJson(prodJson, Product::class.java)
println(product)
it.reply("SUCCESS")
}
}
else -> {
print("ERROR")
}
}
}
startFuture.complete()
}
data class Product(
#SerializedName("id") val id: Int,
#SerializedName("name") val name: String,
#SerializedName("productCode") val productCode: String
)
}
Tested with:
val vertx = Vertx.vertx()
vertx.deployVerticle(DataVerticle()) {
val options = DeliveryOptions()
options.addHeader("ACTION", "ADD_PRODUCT")
vertx.eventBus().send("data.verticle", """{"id":1,"name":"SOAP","productCode":"P101"}""", options)
}
This is annotation definition:
#Target(AnnotationTarget.PROPERTY)
#Retention(AnnotationRetention.RUNTIME)
#MustBeDocumented
annotation class MyAnno(val desc: String, val comment: String) { }
And below is where the MyAnno used:
class MyAnnoUser {
#MyAnno(desc = "name", comment = "name comment")
lateinit var name: String
#MyAnno(desc = "age", comment = "age comment")
var age: Int = 0
#MyAnno(desc = "money", comment = "money comment")
var money: Double = 0.0
#MyAnno(desc = "gender", comment = "gender comment")
var gender: Boolean = false
override fun toString(): String {
return "(name: $name; age: $age; money: $money; gender: ${if (gender) "men" else "women"})"
}
}
Here's code to read the value in MyAnno:
class MyAnnoExpression(val obj: Any, val context: Context) {
val numTypeSet = setOf("Int", "Double", "Byte")
fun expression() {
val clazz = obj::class
clazz.declaredMemberProperties.forEach { prop ->
val mutableProp = try {
prop as KMutableProperty<*>
} catch (e: Exception) {
null
} ?: return#forEach
val desc = mutableProp.findAnnotation<MyAnno>()
desc?.let {
val propClassName = mutableProp.returnType.toString().removePrefix("kotlin.")
when (propClassName) {
in numTypeSet -> mutableProp.setter.call(obj, (readProp(it, context) as kotlin.String).toNum(propClassName))
"String" -> mutableProp.setter.call(obj, (readProp(it, context) as kotlin.String))
"Boolean" -> mutableProp.setter.call(obj, (readProp(it, context) as kotlin.String).toBoolean())
}
}
}
}
private fun readProp(value: MyAnno, context: Context): Any? {
val prop = Properties()
val input = context.assets.open("app.properties")
prop.load(InputStreamReader(input, "utf-8"))
return prop.get(value.desc)
}
}
Now the Debugger shows me following info of value in readProp(...) function:
#com.demo.basekotlin.MyAnno(comment=age comment, desc=age)
But i got exception when read desc from value:
An exception occurs during Evaluate Expression Action : org.jetbrains.eval4j.VOID_VALUE cannot be cast to org.jetbrains.eval4j.AbstractValue
I can't find any thing wrong in my code, is there another program setting needed?
As I understand you just want to see annotation value for given property.
First, let's declare an annotation.
#Target(PROPERTY)
#Retention(AnnotationRetention.RUNTIME)
annotation class PropertyAnnotation(val desc: String)
Container:
class Container {
#PropertyAnnotation("Name")
var name: String? = null
#PropertyAnnotation("Age")
var age: Int = -1
var notAnnotatedProperty: String = "not annotated"
}
And finally, code responsible for get all declared properties, then find a properties annotated as PropertyAnnotation, cast it to it, and get value from it.
fun main() {
val container = Container()
container::class.declaredMemberProperties.forEach { property ->
(property.annotations.find {
it is PropertyAnnotation
} as? PropertyAnnotation)?.let {
println("Property: `$property` is ${it.desc}")
}
}
}
Output:
Property: `var Container.age: kotlin.Int` is Age
Property: `var Container.name: kotlin.String?` is Name
Kind ugly. But, let's use more Kotlin pro-dev-features.
Let's create extension function for any not-null type which returns all member property of given type:
inline fun <reified T : Any> Any.getMemberProperty(): List<T> {
return this::class.declaredMemberProperties.mapNotNull { prop ->
(prop.annotations.find { ann -> ann is T }) as? T
}
}
And now usage:
fun main() {
val container = Container()
container.getMemberProperty<PropertyAnnotation>().forEach {
println(it.desc)
}
}