How to parse a JSON string into a JSONObject in Kotlin?

Question

I recently started a project in Kotlin with Android Studio.

So, I have a problem with a JSON object. I get data from an BroadcastReceiver object, a String to be more specific, with the next format:

{"s1":1}

This, is a simple string. So I took in a function call toJson and I do this.

private fun toJson(data:String): JSONObject {
    
    var newData: String = data.replace("\"","")
    newData = newData.replace("{","")
    newData = newData.replace("}","")

    val newObject = newData.split(":")
    val name = newObject[0]
    val value = newObject[1]
    val rootObject = JSONObject()
    rootObject.put(name,value)

    return rootObject
}

Am I doing this the right way? How can I improve my code?

Im doing this the right way? no, this is not feasible for more complex data. You can probably create a JSONObject from a string directly. Try JSONObject(data) — Tim
– Tim, Commented Sep 25, 2019 at 14:41
You should check this thread. stackoverflow.com/questions/51777441/… — Hritik Gupta
– Hritik Gupta, Commented Sep 25, 2019 at 14:48
If one of the answers was helpful for you then I suggest you to mark it as accepted below the voting. — GV_FiQst
– GV_FiQst, Commented Sep 25, 2019 at 15:48

Nimantha · Accepted Answer · 2023-11-11 06:23:14Z

31

In 2019 no-one is really parsing JSON manually. It's much easier to use Gson library. It takes as an input your object and spits out JSON string and vice-versa.

Example:

data class MyClass(@SerializedName("s1") val s1: Int)

val myClass: MyClass = Gson().fromJson(data, MyClass::class.java)
val outputJson: String = Gson().toJson(myClass)

This way you're not working with JSON string directly but rather with Kotlin object which is type-safe and more convenient. Look at the docs. It's pretty big and easy to understand

Here is some tutorials:

UPDATE: If you really want to use JSONObject then use its constructor with a string parameter which parses your JSON string automatically.

val jsonObject = JSONObject(data)

edited Nov 11, 2023 at 6:23

Nimantha

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answered Sep 25, 2019 at 14:53

GV_FiQst

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5 Comments

a_local_nobody Over a year ago

in all honesty gson should be part of android by now

Alexey Romanov Over a year ago

Or Moshi (see stackoverflow.com/questions/43577623/moshi-vs-gson-in-android and reddit.com/r/androiddev/comments/684flw/why_use_moshi_over_gson/… in particular)

Talha Over a year ago

its 2022 and i am still surprised we cant write JSON directly in Kotlin backed by some DSL features. (Just like we can create objects in JS by simply using {} )

reducing activity Over a year ago

For me it compiles and then fails on execution with java.lang.ClassNotFoundException: org.gradle.internal.impldep.com.google.gson.Gson

GV_FiQst Over a year ago

Gson is located inside com.google.gson package. The package in your exception message is different so I guess you just didn't set it up correctly. Please refer to the official documentation.

fisio · Accepted Answer · 2020-11-29 22:39:53Z

Best way is using kotlinx.serialization. turn a Kotlin object into its JSON representation and back marking its class with the @Serializable annotation, and using the provided encodeToString and decodeFromString<T> extension functions on the Json object:

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

@Serializable
data class User(val name: String, val yearOfBirth: Int)

   // Serialization (Kotlin object to JSON string)

   val data = User("Louis", 1901)
   val string = Json.encodeToString(data)
   println(string) // {"name":"Louis","yearOfBirth":1901}

   // Deserialization (JSON string to Kotlin object)

   val obj = Json.decodeFromString<User>(string)
   println(obj) // User(name=Louis, yearOfBirth=1901)

Further examples: https://blog.jetbrains.com/kotlin/2020/10/kotlinx-serialization-1-0-released/

Takermania · Accepted Answer · 2019-09-25 15:19:18Z

I am adding 3 templates here for Kotlin Developers, It will solve json converting & parsing problems.

//Json Array template
{
  "json_id": "12.4",
  "json_name": "name of the array",
  "json_image": "https://image_path",
  "json_description": "Description of the Json Array"
}

Kotlin Model class

data class JsonDataParser(
  @SerializedName("json_id") val id: Long, 
  @SerializedName("json_name") val name: String, 
  @SerializedName("json_image") val image: String,
  @SerializedName("json_description") val description: String
)

Converting to Json String from the Model Class

val gson = Gson()
val json = gson.toJson(jsonDataParser)

Parsing from Json file/Strong

val json = getJson()
val topic = gson.fromJson(json, JsonDataParser::class.java)

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