Json
- Kotlin course
- Advanced
- Lesson 26/83
- 5 min
Learn Json.encodeToString and decodeFromString.
The Json object
Json is the object that produces and reads JSON with kotlinx.serialization. Json.encodeToString(value) produces JSON, Json.decodeFromString<T>(text) reads JSON.
Example: val json = Json.encodeToString(user). This turns user into {"name":"Alex"}. With Json { prettyPrint = true } you configure it. The default Json object produces compact JSON. decodeFromString<User>(json) declares the target class via the type parameter.
decodeFromString
decodeFromString turns a JSON string into a Kotlin object. The type parameter declares the target class.
Example: val user = Json.decodeFromString<User>("{"name":"Alex"}"). This turns the JSON string into a User object. JSON field names must match Kotlin property names. Mismatched fields throw. With ignoreUnknownKeys = true unknown fields are skipped. This is useful for external JSON.
Practice Use Json encodeToString
Define @Serializable data class User(val name: String). Inside main, set val user = User("Alex"), produce JSON with val json = Json.encodeToString(user), and print println("JSON produced").
Starter code
// Use Json
// write here
import kotlinx.serialization.Serializable
import kotlinx.serialization.json.Json
fun main() {
}Sample solution
@Serializable
data class User(val name: String)
fun main() {
val user = User("Alex")
val json = Json.encodeToString(user)
println("JSON produced")
}Expected output
JSON produced
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the encodeToString call
val json = Json.____(user)val json = Json.encodeToString(user)Explanation: encodeToString turns an object into JSON.
2 Match Json methods
| Term | Meaning |
|---|---|
encodeToString |
Object to JSON |
decodeFromString |
JSON to object |
Json |
Configuration |
prettyPrint |
Readable output |
3 Which direction does Json.decodeFromString work?
- Object to JSON
- JSON to object Correct answer
- Object to XML
- XML to object
Explanation: decodeFromString turns a JSON string into an object.