Build a Ktor backend as an Android and Kotlin developer

Are you an Android Kotlin developer looking to build your own server? Look no further than Ktor. This powerful tool makes it easy to build asynchronous client and server apps using Kotlin and coroutines. Developed and backed by JetBrains, Ktor is both fun and straightforward. In this article, we’ll give you the rundown on Ktor and share some tips for building your first Ktor app.

Setup

If you’re eager to start building your very first Ktor project, check out the convenient platform provided by http://start.ktor.io. This platform allows you to define your app name, package name, Ktor version, engine, and necessary plugins. For a simple backend that stores data and provides APIs, you’ll need content negotiation and serialization plugins for transforming data transfer objects (data classes) into JSON, as well as routing for communication between the outside world and your Ktor application.

Once you’ve created your app, you’ll find the main entry point (function main), the engine used (in this case, Netty), the address and port, and the serialization and routing configurations. With this basic setup, you’ll be well on your way to building a powerful and effective Ktor app.

DTO

To ensure smooth functionality of your Kotlin-based Ktor application, it is imperative to declare all of your Data Transfer Objects (DTOs) accompanied by their serialized annotation. This helps to optimize the performance of your app and ensure that it is running at its best.

Get routes

When working with Ktor, it is crucial to register the routes within the configureRouting method. There are various types of routes you can work with, including responding to requests, handling URL parameters, and retrieving POST request bodies. By mastering these different route types, you can create a highly functional Ktor application that meets your specific needs.

Discover a basic example of a route that returns an object list below :

Learn now how to create a simple GET route in Ktor that takes parameters in the URL, verifies the parameter, and returns the object or an error if not found. In this example, you’ll see how to handle bad requests and not found errors in Ktor.

call.parameters["param"] gets the param passed in the call

Post route with a body

To ensure that all customer properties such as id, firstName, lastName, and email are present, use call.receive to wait for the exact JSON body.

Authentication

Adding authentication to your Ktor app is crucial. You can start by separating public calls from private ones and wrapping routes with the authenticate lambda. By doing so, if the token bearer is not provided in headers, the authenticate routes will return a 401 error, which indicates that the request is unauthorized.

Conclusion and tips

As a final recommendation, we suggest utilizing Insomnia to build your APIs. This powerful tool makes it easy to create, test, maintain, and document your APIs. We truly hope that this guide has inspired you to start building your very own Ktor application today! Whether you’re an experienced developer or just starting out, Ktor is a powerful tool that can help you take your projects to the next level.

If you want to have Ktor ready to use with a whole template for your Android and iOS application then you might be interested in AppKickstarter.