Ktor Framework Cheatsheet

Ktor is a modern, asynchronous web framework for building backend applications in Kotlin. It is designed to be concise, expressive, and easy to use. Whether you’re a seasoned developer or just getting started with Ktor, having a cheatsheet can be incredibly handy. In this blog post, we’ll provide a quick reference guide code snippets to help you navigate the essentials of the Ktor framework.

Getting Started

Installation

To get started with Ktor, you need to add the necessary dependencies to your project. This can be done using a build tool like Gradle or Maven. Here’s an example for Gradle:

// build.gradle.kts

plugins {
    kotlin("jvm") version "1.5.20"
    application
}

application {
    mainClassName = "com.example.ApplicationKt"
}

dependencies {
    implementation "io.ktor:ktor-server-netty:1.6.4"
    implementation "io.ktor:ktor-html-builder:1.6.4"
    implementation "io.ktor:ktor-features:1.6.4"
    implementation "io.ktor:ktor-gson:1.6.4"
}

Application Setup

Now, let’s set up a basic Ktor application. Create a Kotlin file (e.g., Application.kt) with the following code:

// Application.kt

import io.ktor.application.*
import io.ktor.features.ContentNegotiation
import io.ktor.features.StatusPages
import io.ktor.http.ContentType
import io.ktor.http.HttpStatusCode
import io.ktor.jackson.jackson
import io.ktor.request.receive
import io.ktor.response.respond
import io.ktor.routing.*
import io.ktor.server.engine.embeddedServer
import io.ktor.server.netty.Netty

fun main() {
    embeddedServer(Netty, port = 8080) {
        install(ContentNegotiation) {
            jackson {
                // Configure Jackson here if needed
            }
        }

        install(StatusPages) {
            exception<Throwable> { cause ->
                call.respond(HttpStatusCode.InternalServerError, cause.localizedMessage)
            }
        }

        routing {
            // Define your routes here
        }
    }.start(wait = true)
}

Routing

Basic Routing

Ktor provides a simple and expressive way to define routes. Here’s an example:

routing {
    route("/api") {
        get("/hello") {
            call.respondText("Hello, Ktor!")
        }
    }
}

Path Parameters

You can easily extract path parameters from the URL:

routing {
    get("/user/{id}") {
        val userId = call.parameters["id"]
        call.respondText("User ID: $userId")
    }
}

Handling Requests and Responses

Request Body

To handle incoming JSON requests, use the receive function:

data class User(val name: String, val age: Int)

routing {
    post("/user") {
        val user = call.receive<User>()
        call.respondText("Received user: $user")
    }
}

Responding with JSON

Use the respond function to send JSON responses:

routing {
    get("/user") {
        val user = User("John Doe", 25)
        call.respond(user)
    }
}

This cheatsheet provides a quick reference guide for some fundamental aspects of the Ktor framework. As you explore Ktor further, you’ll discover more features and capabilities that make it a powerful choice for building modern, asynchronous web applications in Kotlin.

FAQ