I would like to have custom names when writing my object but it's not printing what I have defined in annotation #JsonProperty:
data class Banking(
#JsonProperty("personita_id")
val clientId: String?,
#JsonProperty("contita_id")
val accountId: String?
)
val mapper = ObjectMapper()
val xpto = mapper.writeValueAsString(Banking("mammamia", "miaccuenta"))
xpto prints:
{"clientId": "mammamia", "accountId": "miaccuenta"}
What is missing in my code?
You can register the KotlinModule on the ObjectMapper from jackson-module-kotlin
val mapper = ObjectMapper().registerModule(KotlinModule())
or depending on the used version
val mapper = ObjectMapper().registerKotlinModule();
Related
How can I achieve, using Moshi library, the same output (toJson) as Gson library, which would contain all fields from the object's class as well as from all its superclasses?
The real environment is more complex, but lets assume the following classes:
#JsonClass(generateAdapter = true)
open class Entity(
val type: String,
val id: String = "",
val comment: String
)
#JsonClass(generateAdapter = true)
open class Animal(
val name: String,
val description: String
): Entity(
type = "animal",
comment = "living"
)
And assume the following testing code, showing what I tried:
fun testJson() {
val dog = Animal("dog", "friendly")
val moshi = Moshi.Builder().build()
println("moshi as Animal: " + moshi.adapter(Animal::class.java).lenient().serializeNulls().failOnUnknown().toJson(dog))
println("moshi as Entity: " + moshi.adapter(Entity::class.java).lenient().serializeNulls().failOnUnknown().toJson(dog))
val moshiWithPoly = Moshi.Builder()
.add(
PolymorphicJsonAdapterFactory.of(Entity::class.java, "type")
.withSubtype(Animal::class.java, "animal"))
.add(KotlinJsonAdapterFactory())
.build()
println("moshi with Poly: " + moshiWithPoly.adapter(Entity::class.java).lenient().serializeNulls().failOnUnknown().toJson(dog))
val gson = Gson()
println("gson: " + gson.toJson(dog))
}
The function generates the following, showing that all the moshi attempts are discarding some of the fields.
moshi as Animal: {"name":"dog","description":"friendly"}
moshi as Entity: {"type":"animal","id":"","comment":"living"}
moshi with Poly: {"type":"animal","name":"dog","description":"friendly"}
gson: {"name":"dog","description":"friendly","type":"animal","id":"","comment":"living"}
How can I achieve same output from moshi as from gson lib?
I have the following dataclasses:
data class JsonNpc(
val name: String,
val neighbours: JsonPreferences
)
data class JsonPreferences(
val loves: List<String>,
val hates: List<String>
)
I have a list of these, and they reference each other through strings like:
[
JsonNpc(
"first",
JsonPreferences(
listOf("second"),
listOf()
)
),
JsonNpc(
"second",
JsonPreferences(
listOf(),
listOf("first")
)
)
]
note that a likes b does not mean b likes a
I also have the Dataclasses
data class Npc(
val name: String,
val neighbours: NeighbourPreferences,
)
data class NeighbourPreferences(
val loves: List<Npc>,
val hates: List<Npc>
)
And I want to convert the String reference types to the normal reference types.
What I have tried:
recursively creating the npcs (and excluding any that are already in the chain, as that would lead to infinite recursion):
Does not work, as the Npc can not be fully created and the List is immutable (I dont want it to be mutable)
I have managed to find a way to do this. It did not work with Npc as a data class, as I needed a real constructor
fun parseNpcs(map: Map<String, JsonNpc>): Map<String, Npc> {
val resultMap: MutableMap<String, Npc> = mutableMapOf()
for (value in map.values) {
if(resultMap.containsKey(value.name))
continue
Npc(value, map, resultMap)
}
return resultMap
}
class Npc(jsonNpc: JsonNpc, infoList: Map<String, JsonNpc>, resultMap: MutableMap<String, Npc>) {
val name: String
val neighbourPreferences: NeighbourPreferences
init {
this.name = jsonNpc.name
resultMap[name] = this
val lovesNpc = jsonNpc.neighbours.loves.map {
resultMap[it] ?: Npc(infoList[it] ?: error("Missing an Npc"), infoList, resultMap)
}
val hatesNpc = jsonNpc.neighbours.hates.map {
resultMap[it] ?: Npc(infoList[it] ?: error("Missing an Npc"), infoList, resultMap)
}
this.neighbourPreferences = NeighbourPreferences(
lovesNpc, hatesNpc
)
}
}
data class NeighbourPreferences(
val loves: List<Npc>,
val hates: List<Npc>
)
checking in the debugger, the people carry the same references for each Neighbour, so the Guide is always one Npc instance.
I'm new to Kotlin & understanding the concepts as I move. Stuck in creating one type of Data class model where the response json structure as shown below
data class SPLPlayer(
#field:Json(name ="id") val playerId: String?,
val type: String?,
#field:Json(name ="value") val currentValue: String?,
#field:Json(name ="Confirm_XI") val isIn_XI: Boolean = false,
#field:Json(name ="Matches") val totalMatchs: String?,
#field:Json(name ="Position") val position: String?,
#field:Json(name ="Skill") val skill: String?,
#field:Json(name ="skill_name") val skillName: String?,
val teamId: String?,
val name: String?, // other keys to refer Name_Full, short_name
#field:Json(name ="Bowling") val bowler: SPLBowler? = null,
#field:Json(name ="Batting") val batsmen: SPLBatsmen? = null
)
data class SPLTeamInfo (
**How to parse the Team object which is dictionary**
)
Thanks & appreciate to every reader. Looking forward for the solution.
You should be able to use your own deserializer by adding annotation to a setter #set:JsonDeserialize() and passing your own deserializer implementation.
along the lines of:
import com.fasterxml.jackson.databind.annotation.JsonDeserialize
import com.fasterxml.jackson.databind.JsonDeserializer
.. rest of imports
// for a given simplified json string
val json: String = """{"teams":{"1":{"name":"foo"},"2":{"name":"bar"}}}"""
class MyDeserializer : JsonDeserializer<List<Team>> {
override fun deserialize(json: JsonElement?, typeOfT: Type?, context: JsonDeserializationContext?): List<Team>? {
// iterate over each json element and return list of parsed teams
}
}
data class JsonResp (
#set:JsonDeserialize(using = MyDeserializer::class)
var teams: List<Team>
)
data class Team (
var id: String, // this is going to be a team key
var name: String
)
Tried GitHub search with query #set:JsonDeserialize and it shows thousands of examples.
With kotlinx.serialization polymorphism, I want to get
{"type":"veh_t","owner":"Ivan","bodyType":"cistern","carryingCapacityInTons":5,"detachable":false}
but I get
{"type":"kotlin.collections.LinkedHashMap","owner":"Ivan","bodyType":"cistern","carryingCapacityInTons":5,"detachable":false}
I use the following models
interface Vehicle {
val owner: String
}
#Serializable
#SerialName("veh_p")
data class PassengerCar(
override val owner: String,
val numberOfSeats: Int
) : Vehicle
#Serializable
#SerialName("veh_t")
data class Truck(
override val owner: String,
val body: Body
) : Vehicle {
#Serializable
data class Body(
val bodyType: String,
val carryingCapacityInTons: Int,
val detachable: Boolean
//a lot of other fields
)
}
I apply the following Json
inline val VehicleJson: Json get() = Json(context = SerializersModule {
polymorphic(Vehicle::class) {
PassengerCar::class with PassengerCar.serializer()
Truck::class with TruckKSerializer
}
})
I use serializer TruckKSerializer because the server adopts a flat structure. At the same time, in the application I want to use an object Truck.Body. For flatten I override fun serialize(encoder: Encoder, obj : T) and fun deserialize(decoder: Decoder): T in Serializator using JsonOutput and JsonInput according to the documentation in these classes.
object TruckKSerializer : KSerializer<Truck> {
override val descriptor: SerialDescriptor = SerialClassDescImpl("Truck")
override fun serialize(encoder: Encoder, obj: Truck) {
val output = encoder as? JsonOutput ?: throw SerializationException("This class can be saved only by Json")
output.encodeJson(json {
obj::owner.name to obj.owner
encoder.json.toJson(Truck.Body.serializer(), obj.body)
.jsonObject.content
.forEach { (name, value) ->
name to value
}
})
}
#ImplicitReflectionSerializer
override fun deserialize(decoder: Decoder): Truck {
val input = decoder as? JsonInput
?: throw SerializationException("This class can be loaded only by Json")
val tree = input.decodeJson() as? JsonObject
?: throw SerializationException("Expected JsonObject")
return Truck(
tree.getPrimitive("owner").content,
VehicleJson.fromJson<Truck.Body>(tree)
)
}
}
And finally, I use stringify(serializer: SerializationStrategy<T>, obj: T)
VehicleJson.stringify(
PolymorphicSerializer(Vehicle::class),
Truck(
owner = "Ivan",
body = Truck.Body(
bodyType = "cistern",
carryingCapacityInTons = 5,
detachable = false
)
)
)
I end up with {"type":"kotlin.collections.LinkedHashMap", ...}, but I need {"type":"veh_t", ...}
How do I get the right type? I want using polymorphism for Vehicle and encode Body object with Truck.Body.serializer() to flatten.
With this serialization, the PassengerCar class runs fine.
VehicleJson.stringify(
PolymorphicSerializer(Vehicle::class),
PassengerCar(
owner = "Oleg",
numberOfSeats = 4
)
)
Result is correct:
{"type":"veh_p","owner":"Oleg","numberOfSeats":4}
I think the problem is the custom serializer TruckKSerializer.
And I noticed if I use in my overridden fun serialize(encoder: Encoder, obj : T) next code
encoder
.beginStructure(descriptor)
.apply {
//...
}
.endStructure(descriptor)
I get the correct type but cannot flatten the object Truck.Body using its serializer.
the correct way to open and close a composite {}
is this code
val composite = encoder.beginStructure(descriptor)
// use composite instead of encoder here
composite.endStructure(descriptor)
and you should be able to serialize Body using .encodeSerializable(Body.serializer(), body)
and always pass the descriptor along otherwise it will fall back to stuff like that LinkedhashMap for the json dictionary
Let's take the class of a data class:
data class User(
val userNumber: Int = -1,
val name: String,
val userGroups; List<String> = emptyList(),
val screenName: String = "new-user"
)
When calling this function from Kotlin, it is pretty straightforward. I can simply use the named-argument syntax to do so. Calling from Java, I have to specify all values, or use the #JvmOverloads annotation, which generates the following constructors (in addition to the constructor that kotlin generates with the bit-mask for default values):
User(int userNumber, #NotNull String name, #NotNull List userGroups,
#NotNull String screenName)
User(int userNumber, #NotNull String name, #NotNull List userGroups)
User(int userNumber, #NotNull String name)
User(#NotNull String name)
Now, if I want to create a User object in Java equivalent to User(name="John Doe", userGroups=listOf("admin", "super") I can't do it with the above constructors. I CAN however do it if I put val userNumber: Int = -1 at the end in the data class declaration (the generation of constructors seems to depend on the order the optional arguments are defined in). Which is fine, because expecting kotlin to generate all permutations is going to heavily bloat some classes.
The biggest problem that tools like Jackson simply don't work as they have no idea which constructor to use (and not like I can annotate one of the generated ones specially).
So, is there a way to generate a (single) constructor like:
User(Integer userNumber, String name, List<String> userGroups, String screenName) {
this.userNumber = (userNumber == null) ? -1 : userNumber;
this.userGroups = (userGroups == null) ? Collections.emptyList() : userGroups;
//...
}
Currently I am using the above approach, but manually defining the constructors where I need them.
EDIT
I should clarify, creating a similar constructor doesn't work, obviously because both the signatures would clash on the JVM. This is what it would like in my case:
data class User(
val userNumber: Int = -1,
val name: String,
val userGroups; List<String> = emptyList(),
val screenName: String = "new-user"
) {
companion object {
#JvmStatic
#JsonCreator
fun constructionSupport(
#JsonProperty("userNumber") userNumber : Int?,
#JsonProperty("name") name : String,
#JsonProperty("userGroups") userGroups : List<String>?,
#JsonProperty("screenName") screenName : String?
) = User(
userNumber = userNumber ?: -1,
name = name,
userGroups = userGroups ?: emptyList(),
screenName = screenName ?: "new-user"
)
}
}
Also note the redundancy where I have to write the default values for the properties twice. I Now that I look at it, I doubt there exists a solution for this. Maybe this is a good use-case for a kapt based side-project of mine :)
Better solution is to add possibility to library understand Kotlin functional. For example, for Jackson exists jackson-module-kotlin. With this library we can use default arguments in data classes.
Example:
data class User(
val userNumber: Int = -1,
val name: String,
val userGroups: List<String> = emptyList(),
val screenName: String = "new-user"
)
fun main(args: Array<String>) {
val objectMapper = ObjectMapper()
.registerModule(KotlinModule())
val testUser = User(userNumber = 5, name = "someName")
val stringUser = objectMapper.writeValueAsString(testUser)
println(stringUser)
val parsedUser = objectMapper.readValue<User>(stringUser)
println(parsedUser)
assert(testUser == parsedUser) {
println("something goes wrong")
}
}
After kicking this around for a minute, I think I found a solution that may work well here. Simply define a top level function in the same source file, that will build the object. Perhaps like so:
fun build_user(userNumber: Int?, name: String, userGroups: List<String>?, screenName: String?) : User {
return User(if(userNumber !== null) userNumber else -1, name, if(userGroups !== null) userGroups else emptyList(),
if(screenName !== null) screenName else "new-user")
}
Then when you need it, you simply call it from Java:
User user = UserKt.build_user(null, "Hello", null, "Porterhouse Steak");
System.out.println(user);
Output from the example:
User(userNumber=-1, name=Hello, userGroups=[], screenName=Porterhouse Steak)
The method is somewhere between a constructor and a builder. It beats hammering out a full-blown Builder object, and avoids cluttering your data class with unnecessary Java-interop glue code messiness.
See Package Level Functions for more information.