Làm việc với JSON trong Kotlin

// build.gradle.kts
plugins {
    kotlin("plugin.serialization") version "1.9.0"
}
 
dependencies {
    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0")
}

import kotlinx.serialization.*
import kotlinx.serialization.json.*
 
@Serializable
data class User(val name: String, val age: Int)
 
fun main() {
    val user = User("Alice", 25)
    val json = Json.encodeToString(user)
    println(json)  // {"name":"Alice","age":25}
}

import kotlinx.serialization.*
import kotlinx.serialization.json.*
 
@Serializable
data class User(val name: String, val age: Int)
 
fun main() {
    val jsonString = """{"name":"Bob","age":30}"""
    val user = Json.decodeFromString<User>(jsonString)
    println(user)  // User(name=Bob, age=30)
}

@Serializable
data class Address(val city: String, val country: String)
 
@Serializable
data class Person(val name: String, val address: Address)
 
fun main() {
    val json = """
        {
            "name": "Alice",
            "address": {
                "city": "Hanoi",
                "country": "Vietnam"
            }
        }
    """.trimIndent()
    
    val person = Json.decodeFromString<Person>(json)
    println(person.address.city)  // Hanoi
}

@Serializable
data class User(val name: String)
 
fun main() {
    val json = """[{"name":"Alice"},{"name":"Bob"}]"""
    
    val users = Json.decodeFromString<List<User>>(json)
    users.forEach { println(it.name) }
}

@Serializable
data class Config(
    val host: String = "localhost",
    val port: Int = 8080,
    val debug: Boolean = false
)
 
fun main() {
    val json = """{"host":"api.example.com"}"""
    val config = Json.decodeFromString<Config>(json)
    
    println(config.host)   // api.example.com
    println(config.port)   // 8080 (default)
}

val json = Json {
    prettyPrint = true
    ignoreUnknownKeys = true
    isLenient = true
    encodeDefaults = true
}
 
@Serializable
data class User(val name: String)
 
fun main() {
    val user = User("Alice")
    println(json.encodeToString(user))
    // Pretty printed output
}

import kotlinx.serialization.*
import kotlinx.serialization.descriptors.*
import kotlinx.serialization.encoding.*
 
object DateAsLongSerializer : KSerializer<Date> {
    override val descriptor = PrimitiveSerialDescriptor("Date", PrimitiveKind.LONG)
    
    override fun serialize(encoder: Encoder, value: Date) {
        encoder.encodeLong(value.time)
    }
    
    override fun deserialize(decoder: Decoder): Date {
        return Date(decoder.decodeLong())
    }
}
 
@Serializable
data class Event(
    val name: String,
    @Serializable(with = DateAsLongSerializer::class)
    val date: Date
)

// Add: implementation("com.google.code.gson:gson:2.10.1")
 
import com.google.gson.Gson
 
data class User(val name: String, val age: Int)
 
fun main() {
    val gson = Gson()
    
    // To JSON
    val user = User("Alice", 25)
    val json = gson.toJson(user)
    
    // From JSON
    val parsed = gson.fromJson(json, User::class.java)
    println(parsed)
}