Kotlin Serialization

Converting Kotlin objects to JSON and other formats

📦 What is Kotlin Serialization?

Kotlin Serialization is a compiler plugin that automatically generates serialization code for your data classes. Convert objects to JSON, XML, or other formats effortlessly and safely. 


@Serializable
data class Person(val name: String, val age: Int)

val person = Person("Alice", 25)
val json = Json.encodeToString(person)
// Result: {"name":"Alice","age":25}

Serialization Features

🔄

JSON Support

Built-in JSON serialization 

Json.encodeToString(data)
Json.decodeFromString<Person>(json)
🛡️

Type Safety

Compile-time type checking 

@Serializable
data class User(val id: Int)
⚙️

Customization

Custom serializers and names 

@SerialName("user_name")
val userName: String
🌐

Multiple Formats

JSON, XML, ProtoBuf support 

ProtoBuf.encodeToByteArray(data)
Xml.encodeToString(data)

🔹 Basic Serialization

Mark your data classes with @Serializable: 

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

@Serializable
data class Book(
    val title: String,
    val author: String,
    val pages: Int,
    val published: Boolean = false
)

fun main() {
    val book = Book("1984", "George Orwell", 328, true)
    
    // Serialize to JSON
    val json = Json.encodeToString(book)
    println(json)
    
    // Deserialize from JSON
    val bookFromJson = Json.decodeFromString<Book>(json)
    println(bookFromJson)
}

Output: 

{"title":"1984","author":"George Orwell","pages":328,"published":true}
Book(title=1984, author=George Orwell, pages=328, published=true)

🔹 Custom Property Names

Use @SerialName to customize JSON property names: 

@Serializable
data class User(
    @SerialName("user_id")
    val id: Int,
    
    @SerialName("full_name")
    val name: String,
    
    @SerialName("email_address")
    val email: String
)

fun main() {
    val user = User(1, "John Doe", "[email protected]")
    val json = Json.encodeToString(user)
    println(json)
}

Output: 

{"user_id":1,"full_name":"John Doe","email_address":"[email protected]"}

🔹 Nested Objects and Lists

Serialize complex nested structures: 

@Serializable
data class Address(val street: String, val city: String, val zipCode: String)

@Serializable
data class Company(
    val name: String,
    val employees: List<Employee>,
    val address: Address
)

@Serializable
data class Employee(val name: String, val position: String, val salary: Double)

fun main() {
    val company = Company(
        name = "Tech Corp",
        employees = listOf(
            Employee("Alice", "Developer", 75000.0),
            Employee("Bob", "Designer", 65000.0)
        ),
        address = Address("123 Main St", "Tech City", "12345")
    )
    
    val json = Json {
        prettyPrint = true
    }.encodeToString(company)
    
    println(json)
}

Output: 

{
    "name": "Tech Corp",
    "employees": [
        {
            "name": "Alice",
            "position": "Developer",
            "salary": 75000.0
        },
        {
            "name": "Bob",
            "position": "Designer",
            "salary": 65000.0
        }
    ],
    "address": {
        "street": "123 Main St",
        "city": "Tech City",
        "zipCode": "12345"
    }
}

🔹 Optional and Default Values

Handle optional properties and default values: 

@Serializable
data class Product(
    val id: Int,
    val name: String,
    val price: Double,
    val description: String? = null,  // Optional
    val inStock: Boolean = true       // Default value
)

fun main() {
    // JSON with missing optional fields
    val json = """{"id":1,"name":"Laptop","price":999.99}"""
    
    val product = Json.decodeFromString<Product>(json)
    println(product)
    
    // Serialize with all fields
    val fullProduct = Product(2, "Mouse", 29.99, "Wireless mouse", false)
    println(Json.encodeToString(fullProduct))
}

Output: 

Product(id=1, name=Laptop, price=999.99, description=null, inStock=true)
{"id":2,"name":"Mouse","price":29.99,"description":"Wireless mouse","inStock":false}

🧠 Test Your Knowledge

Which annotation is used to make a class serializable?