Serialization

Serialization is the process of converting a complex object to a format that can be transferred over a network, used by an application, or stored in a database or file.

In Kotlin, serialization tools are made available in kotlinx.serialization. It consists of a few components, the org.jetbrains.kotlin.plugin.serialization Gradle plugin, runtime libraries, and compiler plugins.

Libraries

Kotlin serialization libraries belong to the org.jetbrains.kotlinx: group and begin with kotlinx-serialization- with suffixes that reflect the serialization format, such as json.

Included libraries in kotlinx.serialization for various serialization formats:

• CBOR: kotlin-serialization-cbor
• HOCON: kotlin-serialization-hocon
• Properties: kotlin-serialization-properties
• Protocol buffers: kotlin-serialization-protobuf
• JSON: kotlin-serialization-json

Implementation

@Serializable
class Project(val name: String, val language: String)

An object is first serialized to its primitive values and then encoded to the desired output format. In Kotlin classes must be explicitly marked @Serializable. Below is an example of JSON encoding using json.encodeToString.

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

@Serializable
class Project(val name: String, val language: String)

fun main() {
    val data = Project("kotlinx.serialization", "Kotlin")
    println(Json.encodeToString(data))
}

The output will be:

{"name":"kotlinx.serialization","language":"Kotlin"}

To decode, json.decodeFromString is used:

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

@Serializable
data class Project(val name: String, val language: String)

fun main() {
    val data = Json.decodeFromString<Project>("""
        {"name":"kotlinx.serialization","language":"Kotlin"}
    """)
    println(data)
}

The output will be:

Project(name=kotlinx.serialization, language=Kotlin)

All libraries ,besides JSON serialization, are experimental, for detailed information about serialization formats refer to the Kotlin Serialization Documents and the Kotlin Serialization Guide