Cookbooks
Kotlin
Chapter 10. Data Formats and Serialization
Working with JSON

Kotlin:
Working with JSON

How to:

Kotlin does not include built-in support for JSON but leverages the powerful features of third-party libraries such as Gson by Google and Kotlinx.serialization by JetBrains. Here’s how you can use both to work with JSON.

Using Gson

Add the Gson dependency to your build.gradle file:

implementation 'com.google.code.gson:gson:2.8.9'

Parsing JSON string to an object and vice versa:

import com.google.gson.Gson

// Define a data class
data class User(val name: String, val age: Int)

fun main() {
    val gson = Gson()

    // Serialize
    val json = gson.toJson(User("John Doe", 30))
    println(json)  // Output: {"name":"John Doe","age":30}

    // Deserialize
    val user: User = gson.fromJson(json, User::class.java)
    println(user)  // Output: User(name=John Doe, age=30)
}

Using Kotlinx.serialization

First, include the dependency in your build.gradle:

implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.3.3"

Afterward, apply the kotlinx-serialization plugin at the top of your build script:

plugins {
    kotlin("jvm") version "1.6.10"
    kotlin("plugin.serialization") version "1.6.10"
}

Serializing and deserializing with Kotlinx.serialization:

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

// Define a serializable data class
@Serializable
data class User(val name: String, val age: Int)

fun main() {
    // Serialize
    val json = Json.encodeToString(User("Jane Doe", 28))
    println(json)  // Output: {"name":"Jane Doe","age":28}

    // Deserialize
    val user = Json.decodeFromString<User>(json)
    println(user)  // Output: User(name=Jane Doe, age=28)
}

Both Gson and Kotlinx.serialization simplify working with JSON in Kotlin applications, choosing one over the other depends on your specific project requirements and personal preferences.

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