Kotlin for Backend Development Tutorial: REST API Development with Ktor, Routing, Authentication, and JSON Serialization

This Kotlin for Backend Development tutorial introduces Ktor for building modern, asynchronous REST APIs. It covers Ktor setup, routing, authentication, and JSON serialization using best practices. With clean examples and real-world backend patterns, this chapter helps developers build scalable Kotlin backend services.

Kotlin for Backend Development – Kotlin with Ktor (Complete Tutorial)

Introduction to Ktor

Ktor is a lightweight, asynchronous framework for building Kotlin backend applications using coroutines.

Why Ktor?

  1. Fully asynchronous
  2. Coroutine-based
  3. Simple and flexible
  4. JVM and Native support

Project Setup

Gradle Dependencies (Kotlin DSL)


dependencies {
implementation("io.ktor:ktor-server-core")
implementation("io.ktor:ktor-server-netty")
implementation("io.ktor:ktor-server-content-negotiation")
implementation("io.ktor:ktor-serialization-kotlinx-json")
implementation("io.ktor:ktor-server-auth")
}

REST API Development

Basic Server


fun main() {
embeddedServer(Netty, port = 8080) {
routing {
get("/") {
call.respondText("Hello from Ktor")
}
}
}.start(wait = true)
}

Best Practices

  1. Use layered architecture (routes, services, repositories)
  2. Keep routes thin
  3. Use suspend functions

Routing

Routing defines API endpoints.

Example


routing {
route("/users") {
get {
call.respond(listOf("User1", "User2"))
}
post {
call.respondText("User created")
}
}
}

Best Practices

  1. Group routes logically
  2. Use versioned APIs
  3. Validate inputs

Authentication

Ktor supports multiple authentication methods.

Basic Authentication Example


install(Authentication) {
basic("auth-basic") {
validate { credentials ->
if (credentials.name == "admin" && credentials.password == "password") {
UserIdPrincipal(credentials.name)
} else null
}
}
}

Secured Route


authenticate("auth-basic") {
get("/secure") {
call.respondText("Secure endpoint")
}
}

Best Practices

  1. Use JWT for production
  2. Never store passwords in plain text
  3. Use HTTPS

JSON Serialization

Ktor uses kotlinx.serialization for JSON handling.

Data Model


@Serializable
data class User(val id: Int, val name: String)

Configuration


install(ContentNegotiation) {
json()
}

Responding with JSON


get("/user") {
call.respond(User(1, "Muni"))
}

Best Practices

  1. Use DTOs for API responses
  2. Validate JSON input
  3. Handle serialization errors

Real-World Example: User API


routing {
route("/api/users") {
get {
call.respond(listOf(User(1, "John"), User(2, "Jane")))
}
post {
val user = call.receive<User>()
call.respondText("User ${user.name} added")
}
}
}

Production Best Practices

  1. Use structured logging
  2. Implement global error handling
  3. Add request validation
  4. Enable CORS carefully
  5. Secure APIs with JWT

Chapter Summary

This chapter covered Kotlin backend development using Ktor, including REST API development, routing, authentication, and JSON serialization. These skills enable developers to build fast, scalable, and modern backend services using Kotlin.