How to parse JSON in Kotlin

Question

I m receiving a quite deep JSON object string from a service which I must parse to a JSON object and then map it to classes   How can I transform a JSON string to object in Kotlin   After that the mapping to the respective classes  I was using StdDeserializer from Jackson  The problem arises at the moment the object had properties that also had to be deserialized into classes  I was not able to get the object mapper  at least I didn t know how  inside another deserializer   Thanks in advance for any help  Preferably  natively  I m trying to reduce the number of dependencies I need so if the answer is only for JSON manipulation and parsing it d be enough

User · Answer

There is no question that the future of parsing in Kotlin will be with kotlinx.serialization. It is part of Kotlin libraries. Version kotlinx.serialization 1.0 is finally released

https://github.com/Kotlin/kotlinx.serialization

import kotlinx.serialization.*
import kotlinx.serialization.json.JSON

@Serializable
data class MyModel(val a: Int, @Optional val b: String = "42")

fun main(args: Array<String>) {

    // serializing objects
    val jsonData = JSON.stringify(MyModel.serializer(), MyModel(42))
    println(jsonData) // {"a": 42, "b": "42"}
    
    // serializing lists
    val jsonList = JSON.stringify(MyModel.serializer().list, listOf(MyModel(42)))
    println(jsonList) // [{"a": 42, "b": "42"}]

    // parsing data back
    val obj = JSON.parse(MyModel.serializer(), """{"a":42}""")
    println(obj) // MyModel(a=42, b="42")
}

User · Answer

You can use Gson    Example  Step 1  Add compile   compile  com google code gson gson 2 8 2    Step 2  Convert json to Kotlin Bean use JsonToKotlinClass   Like this   Json data     timestamp    2018-02-13 15 45 45    code    OK    message    user info    path     user info    data          userId   8       avatar     uploads image 20180115 1516009286213053126 jpeg        nickname            gender   0       birthday   1525968000000       age   0       province            city            district            workStatus    Student        userType   0     errorDetail   null     Kotlin Bean  class MineUserEntity        data class MineUserInfo          val timestamp  String          val code  String          val message  String          val path  String          val data  Data          val errorDetail  Any            data class Data          val userId  Int          val avatar  String          val nickname  String          val gender  Int          val birthday  Long          val age  Int          val province  String          val city  String          val district  String          val workStatus  String          val userType  Int           Step 3  Use Gson  var gson   Gson   var mMineUserEntity   gson  fromJson response  MineUserEntity MineUserInfo  class java

User · Answer

This uses kotlinx serialization like Elisha s answer  Meanwhile the API is being stabilized for the upcoming 1 0 release  Note that e g  JSON parse was renamed to Json parse and is now Json decodeFromString  Also it is imported in gradle differently starting in Kotlin 1 4 0  dependencies       implementation  quot org jetbrains kotlinx kotlinx-serialization-core 1 0 0-RC quot    apply plugin   kotlinx-serialization   Example usage   Serializable data class Properties val nid  Int  val tid  Int   Serializable data class Feature val pos  List lt Double gt   val properties  Properties    null       val count  Int    null   Serializable data class Root val features  List lt Feature gt     val root   Json decodeFromString lt Root gt  jsonStr  val rootAlt   Json decodeFromString Root serializer    jsonStr      equivalent  val str   Json encodeToString root      type  Root  can be inferred      For a  top-level  list  does not apply in my case  you would use  val fList   Json decodeFromString lt List lt Feature gt  gt  jsonStr  val fListAlt   Json decodeFromString ListSerializer Feature serializer     jsonStr   Kotlin s data class defines a class that mainly holds data and has  toString   and other methods  e g  destructuring declarations  automatically defined  I m using nullable     types here for optional fields

User · Answer

Without external library  on Android  To parse this  val jsonString    quot  quot  quot                quot type quot   quot Foo quot           quot data quot                              quot id quot  1                quot title quot   quot Hello quot                                         quot id quot  2                quot title quot   quot World quot                                      quot  quot  quot   Use these classes  import org json JSONObject  class Response json  String    JSONObject json        val type  String    this optString  quot type quot       val data   this optJSONArray  quot data quot                 let   0 until it length    map   i - gt  it optJSONObject i         returns an array of JSONObject               map   Foo it toString         transforms each JSONObject of the array into Foo    class Foo json  String    JSONObject json        val id   this optInt  quot id quot       val title  String    this optString  quot title quot      Usage  val foos   Response jsonString

User · Answer

Not sure if this is what you need but this is how I did it  Using import org json JSONObject       val jsonObj   JSONObject json substring json indexOf  quot   quot    json lastIndexOf  quot   quot     1       val foodJson   jsonObj getJSONArray  quot Foods quot       for  i in 0  foodJson   length   - 1            val categories   FoodCategoryObject           val name   foodJson getJSONObject i  getString  quot FoodName quot           categories name   name        Here s a sample of the json     quot Foods quot      quot FoodName quot    quot Apples quot   quot Weight quot    quot 110 quot

User · Answer

i am using my custom implementation in kotlin         Created by Anton Kogan on 10 9 2020     object JsonParser        val TAG    quot JsonParser quot             parse json object     param objJson     param include - all  keys  that you want to display     return  Map lt String  String gt      throws JSONException          Throws JSONException  class      fun parseJson objJson  Any   map  HashMap lt String  String gt   include   Array lt String gt     Map lt String  String gt               If obj is a json array         if  objJson is JSONArray                for  i in 0 until objJson length                      parseJson objJson i   map  include                          else if  objJson is JSONObject                val it  Iterator lt   gt    objJson keys               while  it hasNext                      val key   it next   toString                      If you get an array                 when  val jobject   objJson key                         is JSONArray - gt                            Log e TAG   quot  JSONArray   jobject quot                           parseJson                              jobject  map  include                                                                     is JSONObject - gt                            Log e TAG   quot  JSONObject   jobject quot                           parseJson                              jobject  map  include                                                                     else - gt                               if include    null    include contains key      here is check for include param                                                       map key    jobject toString                               Log e TAG   quot  adding to map   key  jobject quot                                                                                                     return map                       parse json object         param objJson         param include - all  keys  that you want to display         return  Map lt String  String gt          throws JSONException              Throws JSONException  class      fun parseJson objJson  Any   map  HashMap lt String  String gt    Map lt String  String gt            return parseJson objJson  map  null           You can use it like      val include  arrayOf           quot atHome quot    JSONArray          quot cat quot            quot dog quot            quot persons quot    JSONArray          quot man quot            quot woman quot            JsonParser parseJson jsonObject  map  include      val linearContent  LinearLayout   taskInfoFragmentBinding infoContainer  here is some useful links  json parsing   plugin  https   plugins jetbrains com plugin 9960-json-to-kotlin-class-jsontokotlinclass- create POJOs  from json  https   codebeautify org jsonviewer Retrofit  https   square github io retrofit  Gson  https   github com google gson

User · Answer

A bit late  but whatever  If you prefer parsing JSON to JavaScript-like constructs making use of Kotlin syntax  I recommend JSONKraken  of which I am the author  Suggestions and opinions on the matter are much apreciated

User · Answer

GSON is a good choice for Android and Web platform to parse JSON in a Kotlin project  This library is developed by Google  https   github com google gson 1  First add GSON to your project  dependencies      implementation  com google code gson gson 2 8 6     2  Now you need to convert your JSON to Kotlin Data class  Copy your JSON and go to this https   json2kt com  website and paste your JSON to Input Json box  Write package ex  com example appName  and Class name ex  UserData  in proper box  This site will show live preview of your data class below and also you can download all classes at once in a zip file  After downloading all classes extract zip file  amp  place them into your project  3  Now Parse like below  val myJson    quot  quot  quot         quot user name quot    quot john123 quot        quot email quot    quot john example com quot        quot name quot    quot John Doe quot     quot  quot  quot  trimIndent    val gson   Gson   var mUser   gson fromJson myJson  UserData  class java  println mUser userName   Done

User · Answer

Kotin Seriazation Kotlin specific library by Jetbrains for all supported platforms     Android  JVM  JavaScript  Native https   github com Kotlin kotlinx serialization Moshi Moshi is a JSON library for Android and Java by  Square  https   github com square moshi Jackson https   github com FasterXML jackson Gson Most popular but almost deprecated https   github com google gson JSON to Java http   www jsonschema2pojo org  JSON to Kotlin IntelliJ plugin - https   plugins jetbrains com plugin 9960-json-to-kotlin-class-jsontokotlinclass-

User · Answer

First of all   You can use JSON to Kotlin Data class converter plugin in Android Studio for JSON mapping to POJO classes  kotlin data class   This plugin will annotate your Kotlin data class according to JSON   Then you can use GSON converter to convert JSON to Kotlin   Follow this Complete tutorial  Kotlin Android JSON Parsing Tutorial   If you want to parse json manually   val   sampleJson                     userId   1      id   1      title    sunt aut facere repellat provident occaecati excepturi optio      reprehenderit        body    quia et suscipit nsuscipit recusandae consequuntur expedita                 Code to Parse above JSON Array and its object at index 0   var jsonArray   JSONArray sampleJson  for  jsonIndex in 0   jsonArray length   - 1     Log d  JSON   jsonArray getJSONObject jsonIndex  getString  title

User · Answer

You can use this library  https   github com cbeust klaxon  Klaxon is a lightweight library to parse JSON in Kotlin

User · Answer

To convert JSON to Kotlin use http   www json2kotlin com   Also you can use Android Studio plugin  File   Settings  select Plugins in left tree  press  Browse repositories      search  JsonToKotlinClass   select it and click green button  Install      After AS restart you can use it  You can create a class with File  gt  New  gt  JSON To Kotlin Class  JsonToKotlinClass   Another way is to press Alt   K     Then you will see a dialog to paste JSON   In 2018 I had to add package com my package name at the beginning of a class

User · Answer

I personally use the Jackson module for Kotlin that you can find here  jackson-module-kotlin    implementation  com fasterxml jackson module jackson-module-kotlin  version    As an example  here is the code to parse the JSON of the Path of Exile skilltree which is quite heavy  84k lines when formatted     Kotlin code   package util  import com fasterxml jackson databind DeserializationFeature import com fasterxml jackson module kotlin   import java io File  data class SkillTreeData  val characterData  Map lt String  CharacterData gt   val groups  Map lt String  Group gt   val root  Root                            val nodes  List lt Node gt   val extraImages  Map lt String  ExtraImage gt   val min x  Double                            val min y  Double  val max x  Double  val max y  Double                            val assets  Map lt String  Map lt String  String gt  gt   val constants  Constants  val imageRoot  String                            val skillSprites  SkillSprites  val imageZoomLevels  List lt Int gt      data class CharacterData  val base str  Int  val base dex  Int  val base int  Int    data class Group  val x  Double  val y  Double  val oo  Map lt String  Boolean gt    val n  List lt Int gt     data class Root  val g  Int  val o  Int  val oidx  Int  val sa  Int  val da  Int  val ia  Int  val out  List lt Int gt     data class Node  val id  Int  val icon  String  val ks  Boolean  val not  Boolean  val dn  String  val m  Boolean                   val isJewelSocket  Boolean  val isMultipleChoice  Boolean  val isMultipleChoiceOption  Boolean                   val passivePointsGranted  Int  val flavourText  List lt String gt    val ascendancyName  String                    val isAscendancyStart  Boolean   val reminderText  List lt String gt    val spc  List lt Int gt   val sd  List lt String gt                    val g  Int  val o  Int  val oidx  Int  val sa  Int  val da  Int  val ia  Int  val out  List lt Int gt     data class ExtraImage  val x  Double  val y  Double  val image  String    data class Constants  val classes  Map lt String  Int gt   val characterAttributes  Map lt String  Int gt                         val PSSCentreInnerRadius  Int    data class SubSpriteCoords  val x  Int  val y  Int  val w  Int  val h  Int    data class Sprite  val filename  String  val coords  Map lt String  SubSpriteCoords gt     data class SkillSprites  val normalActive  List lt Sprite gt   val notableActive  List lt Sprite gt                            val keystoneActive  List lt Sprite gt   val normalInactive  List lt Sprite gt                            val notableInactive  List lt Sprite gt   val keystoneInactive  List lt Sprite gt                            val mastery  List lt Sprite gt     private fun convert  jsonFile  File         val mapper   jacksonObjectMapper       mapper configure  DeserializationFeature ACCEPT EMPTY ARRAY AS NULL OBJECT  true        val skillTreeData   mapper readValue lt SkillTreeData gt   jsonFile       println  Conversion finished        fun main  args   Array lt String gt          val jsonFile  File   File     rawSkilltree json          convert  jsonFile     JSON  not-formatted   http   filebin ca 3B3reNQf3KXJ rawSkilltree json  Given your description  I believe it matches your needs

User · Answer

http   www jsonschema2pojo org    Hi you can use this website to convert json to pojo    control Alt shift k      After that you can manualy convert that model class to kotlin model class  with                       the help of above  shortcut

User · Answer

Download the source of deme from here Json parsing in android kotlin   Add this dependency   compile  com squareup okhttp3 okhttp 3 8 1    Call api function    fun run url  String        dialog show       val request   Request Builder                url url               build        client newCall request  enqueue object   Callback           override fun onFailure call  Call  e  IOException                dialog dismiss                       override fun onResponse call  Call  response  Response                var str response   response body     string               val json contact JSONObject   JSONObject str response               var jsonarray contacts JSONArray  json contact getJSONArray  contacts                var i Int   0             var size Int   jsonarray contacts length                al details  ArrayList                 for  i in 0   size-1                    var json objectdetail JSONObject jsonarray contacts getJSONObject i                    var model Model  Model                    model id json objectdetail getString  id                   model name json objectdetail getString  name                   model email json objectdetail getString  email                   model address json objectdetail getString  address                   model gender json objectdetail getString  gender                    al details add model                               runOnUiThread                     stuff that updates ui                 val obj adapter   CustomAdapter                 obj adapter   CustomAdapter applicationContext al details                  lv details adapter obj adapter                            dialog dismiss

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