Parse a nested JSON with Kotlinx.Serialization

Question

I've been playing with Kotlinx.serialization, and I have been trying to parse a substring:

Given a JSON like:

{
   "Parent" : {
     "SpaceShip":"Tardis",
     "Mark":40
   }
}

And my code is something like:

data class SomeClass(
   @SerialName("SpaceShip") ship:String,
   @SerialName("Mark") mark:Int)

Obviously, Json.nonstrict.parse(SomeClass.serializer(), rawString) will fail because the pair "SpaceShip" and "Mark" are not in the root of the JSON.

How do I make the serializer refer to a subtree of the JSON?

P.S: Would you recommend retrofit instead (because it's older, and maybe more mature)?

Psijic · Accepted Answer · 2020-04-24 19:44:53Z

2

@Serializable
data class Parent(
    @SerialName("Parent")
    val someClass: SomeClass
)

@Serializable
data class SomeClass(
    @SerialName("SpaceShip")
    val ship: String,
    @SerialName("Mark")
    val mark: Int
)

fun getSomeClass(inputStream: InputStream): SomeClass {
    val json = Json(JsonConfiguration.Stable)
    val jsonString = Scanner(inputStream).useDelimiter("\\A").next()
    val parent = json.parse(Parent.serializer(), jsonString)
    return parent.someClass
}

answered Apr 24, 2020 at 19:44

Psijic

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Comments

Markus · Accepted Answer · 2019-05-11 18:06:13Z

1

import kotlinx.serialization.*
import kotlinx.serialization.json.Json


@Serializable
data class Parent(
    @SerialName("Parent")
    val parent: SomeClass
)

@Serializable
data class SomeClass(
    @SerialName("SpaceShip")
    val ship:String,
    @SerialName("Mark")
    val mark:Int
)

fun main() {
    val parent = Json.parse(Parent.serializer(), "{\"Parent\":{\"SpaceShip\":\"Tardis\",\"Mark\":40}}")
    println(parent)
}

answered May 11, 2019 at 18:06

Markus

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1 Comment

Maneki Neko Over a year ago

Yup, I haven't found a nicer silver bullet. Something that will look exactly like the JSON and describe it nicely. This is, probably, as good as it gets. And then, the question that rings in my mind: Maybe all the comments are right, and simply GSON is just as good?...

Paul Korolyov · Accepted Answer · 2024-06-05 14:29:30Z

1

A solution if parsing different sets of nested data

import kotlinx.serialization.json.Json
import kotlinx.serialization.Serializable

@Serializable
open class topLevel<T>(val a: Int? = null, val b: T? = null)

@Serializable
open class embadedData1(var s: String? = null)

@Serializable
open class variation1() : topLevel<embadedData1>()

fun main() {

    println( Json.decodeFromString( variation1.serializer(),"""{ "a": 1, "b": { "s": "2" } }""").b?.s )
}

edited Jun 5, 2024 at 14:29

answered Jun 5, 2024 at 13:13

Paul Korolyov

112 bronze badges

1 Comment

Community Over a year ago

As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

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