I'm trying to fetch and deserialize some data that is being hosted on github.
{
"Meals": [
{
"id": "1598044e-5259-11e9-8647-d663bd870b02",
"name": "Tomato pasta",
"quantity": [{
"quantity": 1 },
{
"quantity": 2
},
{
"quantity": 3
}],
"availableFromDate": "1605802429",
"expiryDate": "1905802429",
"info": "Vegetarian",
"hot": false,
"locationLat": 57.508865,
"locationLong": -6.292,
"distance": null
},
{
"id": "2be2d854-a067-43ec-a488-2e69f0f2a624",
"name": "Pizza",
"quantity": [{
"quantity": 1 },
{
"quantity": 2
},
{
"quantity": 3
}
],
"availableFromDate": "1605802429",
"expiryDate": "1905902429",
"info": "Meat",
"hot": false,
"locationLat": 51.509465,
"locationLong": -0.135392,
"distance": null
}
]
}
If I spin up a json-server locally then it works perfectly, so I know that my data class is not the problem. However when I try to do the same thing from that github link I get this error:
Error Domain=KotlinException Code=0 "No transformation found: class io.ktor.utils.io.ByteChannelNative -> class kotlin.collections.List
I have a feeling it might be to do with setting a ContentType or something along those lines but I haven't had any success specifying that so far.
Here is my code to make the request:
class MealApi {
private val httpClient = HttpClient {
install(JsonFeature) {
val json = Json { ignoreUnknownKeys = true }
serializer = KotlinxSerializer(json)
}
}
suspend fun getAllMeals(): List<Meal> {
return httpClient.get(endpoint)
}
}
and here is my data class just for completeness:
#Serializable
data class Meal(
#SerialName("id")
val id: String,
#SerialName("name")
val name: String,
#SerialName("quantity")
val quantity: List<Quantity>,
#SerialName("availableFromDate")
var availableFromDate: String,
#SerialName("expiryDate")
var expiryDate: String,
#SerialName("info")
val info: String,
#SerialName("hot")
val hot: Boolean,
#SerialName("locationLat")
val locationLat: Float,
#SerialName("locationLong")
val locationLong: Float,
#SerialName("distance")
var distance: Double? = null
)
#Serializable
data class Quantity(
#SerialName("quantity")
val quantity: Int
)
UPDATE
I've found that this server https://gitcdn.link/ allows you to serve your raw github files with the right Content-Type.
I've searched a lot how to change the server response headers (to change the plain/text one to application/json) but it seems that ktor actually doesn't allow to do that:
https://youtrack.jetbrains.com/issue/KTOR-617
https://youtrack.jetbrains.com/issue/KTOR-580
A nice way should be to allow the ResponseObserver to change the server response headers and pass through the modify response. But you can't actually.
Your problem depends, as you pointed out, from the fact that the raw github page provides an header Content-Type=plain/text instead of ContentType=application/json.
So IRL when you are running your API in a real server this won't occur as you'll take care to put the right content type at server level.
But if you want a workaround to this you could rewrite your api call in this way:
suspend fun getAllMealsWithFallback() {
var meals: Meals? = null
try {
meals = httpClient.get(endpoint)
} catch (e: NoTransformationFoundException) {
val mealsString: String = httpClient.get(endpoint)
val json = kotlinx.serialization.json.Json {
ignoreUnknownKeys = true
}
meals = json.decodeFromString(mealsString)
} finally {
println("Meals: ${meals?.meals}")
}
}
I had to add this class to conform to the json text you have provided in the github link.
#Serializable
data class Meals(
#SerialName("Meals")
val meals: List<Meal>,
)
Try this:
install(JsonFeature) {
serializer = KotlinxSerializer(KotlinJson { ignoreUnknownKeys = true })
acceptContentTypes = acceptContentTypes + ContentType.Any
}
If you'd like to accept all content types. Or Use ContentType.Text.Any, ContentType.Text.Html if you preferred.
In case the issue is the Content-Type:
You can alter the list of response content types, for which the KotlinxSerializer gets active, by extending the JsonFeature block to:
install(JsonFeature) {
val json = Json { ignoreUnknownKeys = true }
serializer = KotlinxSerializer(json)
receiveContentTypeMatchers += object : ContentTypeMatcher {
override fun contains(contentType: ContentType): Boolean =
contentType == ContentType("text", "plain")
}
}
If you're using Ktor 2.0, you would need ContentNegotiation plugin instead of JsonFeature.
For example if you use Gson:
install(io.ktor.client.plugins.contentnegotiation.ContentNegotiation) {
gson()
}
As a workaround for ktor version 2.0.3 you can create you own AppContentNegotiation class and in the scope.responsePipeline.intercept provide needed contentType
/**
* A plugin that serves two primary purposes:
* - Negotiating media types between the client and server. For this, it uses the `Accept` and `Content-Type` headers.
* - Serializing/deserializing the content in a specific format when sending requests and receiving responses.
* Ktor supports the following formats out-of-the-box: `JSON`, `XML`, and `CBOR`.
*
* You can learn more from [Content negotiation and serialization](https://ktor.io/docs/serialization-client.html).
*/
public class AppContentNegotiation internal constructor(
internal val registrations: List<Config.ConverterRegistration>
) {
/**
* A [ContentNegotiation] configuration that is used during installation.
*/
public class Config : Configuration {
internal class ConverterRegistration(
val converter: ContentConverter,
val contentTypeToSend: ContentType,
val contentTypeMatcher: ContentTypeMatcher,
)
internal val registrations = mutableListOf<ConverterRegistration>()
/**
* Registers a [contentType] to a specified [converter] with an optional [configuration] script for a converter.
*/
public override fun <T : ContentConverter> register(
contentType: ContentType,
converter: T,
configuration: T.() -> Unit
) {
val matcher = when (contentType) {
ContentType.Application.Json -> JsonContentTypeMatcher
else -> defaultMatcher(contentType)
}
register(contentType, converter, matcher, configuration)
}
/**
* Registers a [contentTypeToSend] and [contentTypeMatcher] to a specified [converter] with
* an optional [configuration] script for a converter.
*/
public fun <T : ContentConverter> register(
contentTypeToSend: ContentType,
converter: T,
contentTypeMatcher: ContentTypeMatcher,
configuration: T.() -> Unit
) {
val registration = ConverterRegistration(
converter.apply(configuration),
contentTypeToSend,
contentTypeMatcher
)
registrations.add(registration)
}
private fun defaultMatcher(pattern: ContentType): ContentTypeMatcher =
object : ContentTypeMatcher {
override fun contains(contentType: ContentType): Boolean =
contentType.match(pattern)
}
}
/**
* A companion object used to install a plugin.
*/
#KtorDsl
public companion object Plugin : HttpClientPlugin<Config, AppContentNegotiation > {
public override val key: AttributeKey<AppContentNegotiation> =
AttributeKey("ContentNegotiation")
override fun prepare(block: Config.() -> Unit): AppContentNegotiation {
val config = Config().apply(block)
return AppContentNegotiation(config.registrations)
}
override fun install(plugin: AppContentNegotiation, scope: HttpClient) {
scope.requestPipeline.intercept(HttpRequestPipeline.Transform) { payload ->
val registrations = plugin.registrations
registrations.forEach { context.accept(it.contentTypeToSend) }
if (subject is OutgoingContent || DefaultIgnoredTypes.any { it.isInstance(payload) }) {
return#intercept
}
val contentType = context.contentType() ?: return#intercept
if (payload is Unit) {
context.headers.remove(HttpHeaders.ContentType)
proceedWith(EmptyContent)
return#intercept
}
val matchingRegistrations =
registrations.filter { it.contentTypeMatcher.contains(contentType) }
.takeIf { it.isNotEmpty() } ?: return#intercept
if (context.bodyType == null) return#intercept
context.headers.remove(HttpHeaders.ContentType)
// Pick the first one that can convert the subject successfully
val serializedContent = matchingRegistrations.firstNotNullOfOrNull { registration ->
registration.converter.serialize(
contentType,
contentType.charset() ?: Charsets.UTF_8,
context.bodyType!!,
payload
)
} ?: throw ContentConverterException(
"Can't convert $payload with contentType $contentType using converters " +
matchingRegistrations.joinToString { it.converter.toString() }
)
proceedWith(serializedContent)
}
scope.responsePipeline.intercept(HttpResponsePipeline.Transform) { (info, body) ->
if (body !is ByteReadChannel) return#intercept
if (info.type == ByteReadChannel::class) return#intercept
// !!!!!!! Provide desired content type here
val contentType = <HERE> // default implementation is - context.response.contentType() ?: return#intercept
val registrations = plugin.registrations
val matchingRegistrations = registrations
.filter { it.contentTypeMatcher.contains(contentType) }
.takeIf { it.isNotEmpty() } ?: return#intercept
// Pick the first one that can convert the subject successfully
val parsedBody = matchingRegistrations.firstNotNullOfOrNull { registration ->
registration.converter
.deserialize(context.request.headers.suitableCharset(), info, body)
} ?: return#intercept
val response = HttpResponseContainer(info, parsedBody)
proceedWith(response)
}
}
}
}
And then install it for HttpClient
HttpClient {
install(AppContentNegotiation) {
json(json)
addDefaultResponseValidation()
}
}
In my case, this exception was thrown when I was attempting to access the body() potion of the HTTP response as such:
val httpResponse = httpClient.post(urlString) { ... }
val body = httpResponse.body<YourExpectedSerializableResponseType>
In the happy path scenario, the server would return a body that matched YourExpectedSerializableResponseType and everything would work as expected.
However, for a particular edge case that returned a different (still considered successful) status code, the server returned an empty response body. Since the client was expecting a response body and in this case, there wasn't any, this exception was thrown because it could not serialize an empty response body to the expected type YourExpectedSerializableResponseType.
My recommendation: In addition to ensuring your server is returning the type you expect to serialize/consume on your client, confirm your server is actually returning an object.
Internal Dialogue: I wonder if this exception could be more clear in this case as the issue is more so that the client expected a response body to exist and less so that an empty response body ("") couldn't be serialized into an expected type - especially given that an empty response body isn't even valid JSON. Hm. 🤔
Hi I'm facing problem with serialization of map where key is an custom class.
data class KeyClass(val id: Int, val name: String) {
fun toJSON() = "\"KeyClass\": {\"id\":$id,\"name\":\"$name\"}"
}
Invocation:
fun method(): Map<KeyClass, List<Something>> = ...
My jackson Serializer ofc I'm also adding this as module in objectMapper:
class KeyClassSerializer : JsonSerializer<KeyClass>() {
override fun serialize(value: KeyClass, gen: JsonGenerator, serializers: SerializerProvider) {
gen.writeRawValue(value.toJSON())
}
}
class KeyClassSerializerModule : SimpleModule() {
init {
addKeySerializer(KeyClass::class.java, KeyClassSerializer())
}
}
And JSON I'm receiving is:
"\"KeyClass\": {\"id\":1,\"name\":\"Thomas\"}" : [Something:...]
I mean the value of map is serialized correctly but key isn't.
I assume the expected result is :
"KeyClass": {
"id": 1,
"name":"Thomas"
} : [...]
But it's not valid Json. You can still do something like :
{
"key" : {
"id": 1,
"name":"Thomas"
},
"value" : [...]
}
Sorry but I didn't explain it very well. I edit my question again:
I have an angular 4 application and I use json2typescript to convert from json to object and vice versa but I have a problem because I have a class structure and the response json from an external api has another structure. Example:
Customer {
#JsonProperty('idCardNumber', String)
idCardNumber: string = undefined;
#JsonProperty('rolInfo.name',String)
name: string = undefined;
#JsonProperty('rolInfo.surname',String)
surname: string = undefined;
}
External Json API Reponse:
{
"idCardNumber": "08989765F",
"rolInfo": {
"name": "John"
"surname: "Smith"
}
}
So, I would like to map from the json above to my Customer object and not to change my structure. I tried to put 'rolInfo.name' into the JsonProperty, but that doesn't work.
Change your Customer class to something like below
Customer {
#JsonProperty('idCardNumber', String)
idCardNumber: string = undefined;
#JsonProperty('rolInfo', Any)
rolInfo: any = {}; // if you set this to undefined, handle it in getter/setter
get name(): string {
return this.rolInfo['name'];
}
set name(value: string) {
this.rolInfo['name'] = value;
}
get surname(): string {
return this.rolInfo['surname'];
}
set surname(value: string) {
this.rolInfo['surname'] = value;
}
}
That should do it
Seems like the response JSON is already in a good format and you don’t need to do the conversion.
I would recommend creating models as they allow for serialization and deserialization when making API calls and binding the response to that model.
I am trying to move some code from a grails service file into src/groovy for better reuse.
import grails.converters.JSON
import org.codehaus.groovy.grails.web.json.JSONObject
class JsonUtils {
// seems like a clunky way to accomplish converting a domainObject
// to its json api like object, but couldn't find anything better.
def jsonify(obj, ArrayList removeableKeys = []) {
def theJson = obj as JSON
def reParsedJson = JSON.parse(theJson.toString())
removeableKeys.each { reParsedJson.remove(it) }
return reParsedJson
}
// essentially just turns nested JSONObject.Null things into java null things
// which don't get choked on down the road so much.
def cleanJson(json) {
if (json instanceof List) {
json = json.collect(cleanJsonList)
} else if (json instanceof Map) {
json = json.collectEntries(cleanJsonMap)
}
return json
}
private def cleanJsonList = {
if (it instanceof List) {
it.collect(cleanJsonList)
} else if (it instanceof Map) {
it.collectEntries(cleanJsonMap)
} else {
(it.class == JSONObject.Null) ? null : it
}
}
private def cleanJsonMap = { key, value ->
if (value instanceof List) {
[key, value.collect(cleanJsonList)]
} else if (value instanceof Map) {
[key, value.collectEntries(cleanJsonMap)]
} else {
[key, (value.class == JSONObject.Null) ? null : value]
}
}
}
but when I try to call jsonify or cleanJson from services I get MissingMethodExceptions
example call from grails service file:
def animal = Animal.read(params.animal_id)
if (animal) json.animal = JsonUtils.jsonify(animal, ['tests','vaccinations','label'])
error:
No signature of method: static org.JsonUtils.jsonify() is applicable for argument types: (org.Animal, java.util.ArrayList) values: [ ...]]\ Possible solutions: jsonify(java.lang.Object, java.util.ArrayList), jsonify(java.lang.Object), notify()
Also tried making the jsonify take an animal jsonify(Animal obj, ...) then it just said Possible solutions: jsonify(org.Animal, ...
The cleanJson method was meant to deal with JSONObject.Null things which have caused problems for us before.
example call:
def safeJson = JsonUtils.cleanJson(json) // json is request.JSON from the controller
error:
groovy.lang.MissingMethodException: No signature of method: static org.JsonUtils.cleanJson() is applicable for argument types: (org.codehaus.groovy.grails.web.json.JSONObject) values: [[...]]
Possible solutions: cleanJson(org.codehaus.groovy.grails.web.json.JSONObject)
All this code worked as it is when it was in service file. I am running grails 2.3.11 BTW
You've declared jsonify() and cleanJson() as instance methods and try to use them as static. Declare them as static and it should work:
class JsonUtils {
def static jsonify(obj, ArrayList removeableKeys = []) {
(...)
}
def static cleanJson(json) {
(...)
}
}
You need to define jsonify() and cleanJson() as static in order to call them statically.
I'm using spray and I need to return a json object through a method.
val route =
path("all-modules") {
get {
respondWithMediaType(`text/html`) {
complete( configViewer.findAllModules.toString)
}
}
}
This prints ConfigResults(S1000,Success,List(testDataTypes, mandate, sdp))
But I need get this as the json object. how can I do it?
I tried in this way
val route =
path("all-modules") {
get {
respondWithMediaType(`application/json`) {
complete{
configViewer.findAllModules
}
}
}
}
It gives an compilation error could not find implicit value for parameter marshaller: spray.httpx.marshalling.ToResponseMarshaller
You need to tell Spray how it should serialize your case class.
Just configure something like
object JsonSupport {
implicit val formatConfigResults = jsonFormat3(ConfigResults)
}
The number in jsonFormat'number' stands for the number of members in your case class.
Then you just need to import into your route, the class where you define this implicit.
import JsonSupport._