Build Your First Rest API in Ktor

What is Ktor?

Ktor is a framework build in kotlin language which helps in building web applications, http services etc. Most of the Services needs to fast and secure these days,ktor helps us create asynchronous client and server applications in simple way.

Why Ktor?

Ktor is Lightweight and Flexible framework.
Ktor allows us to use only what we need, and to structure our application the way we need it.
We can easily extend the capability of the framework by using plugins.
As it is coroutine-native thus helps us build large scale server-side applications handling billions of events / day.

Lets Build Our First Rest API in Ktor

To build Rest API in ktor we would need to generate ktor project first, we can do that using the ktor plugin in Ultimate edition of Intellij Idea.

We can also visit https://start.ktor.io and generate the project.

Project Generator you need to add your project name, select server engine and other setting also select plugins we need. For our first API we will need Routing plugin for handling requests and content negotiation to work with Serialization and Deserialization of request Body.

Build Your First Rest API in Ktor | Ktor Rest API - KodeSrc

Unzip the folder created and import the project in the IDE.

KTOR generator will add some sample code to begin with, for our purpose we will remove all the sample code and write our own code in most easy way to get started.

Later on in the subsequent posts we will properly structure our code base and use best coding practices.

Project Structure :

The Initiation point of any app is the main method, here as well we have a main method which will be used to configure our server and set necessary configurations.

We have used HOCON file based configuration approach here.

Application.Kt File:



package kodesrc

import io.ktor.serialization.gson.*
import io.ktor.server.application.*
import io.ktor.server.plugins.contentnegotiation.*
import io.ktor.server.response.*
import io.ktor.server.routing.*

fun main(args: Array <String>) {
    io.ktor.server.netty.EngineMain.main(args)
}

fun Application.initializeApp() {
    install(ContentNegotiation) {
        gson {
        }
    }
    configureRouting()
}
fun Application.configureRouting() {
    routing {
        get("/welcome-to-kodesrc") {
            call.respondText("Welcome to KodeSrc!")
        }
        get("/hello-world") {
            call.respondText("Hello World!")
        }
    }
}

Understanding the Application.Kt File

If we need to use and plugins we need to inform the application to install the library other wise we will not be able to use that particular library functionalities. We have used Gson Library for content negotiation.

The Application Class from io.ktor.server.application package is used and it Represents configured and running web application, capable of handling requests. It is also the application coroutine scope that is cancelled immediately at application stop so useful for launching background coroutines.

The routing{} scope it installs a Routing plugin for the this Application and runs a configuration script on it.

The get ("/welcome-to-kodesrc"){} this is the actual API scope that will get executed when http://localhost:8080/welcome-to-kodesrc URL is hit in browser.

application.conf File:



ktor {
    deployment {
        port = 8080
        port = ${?PORT}
    }
    application {
        modules = [ kodesrc.ApplicationKt.initializeApp ]
    }
}

This is a HOCON file where all the configurations related to the Application is maintained.

That is all you need to create your first Rest API in Ktor. Now run the main method and access the URL in browser.

That is all for this Post. We have easily created our First Rest API in Ktor.

You can find the source code at github here :

KTOR Rest API - WelcomeToKodeSrc

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Build Your First Rest API in Ktor | Ktor Rest API - KodeSrc