Creating a Simple RESTful Web Service Using Kotlin and JetBrains Tools

Introduction

Kotlin, known for its conciseness and compatibility with Java, has gained popularity for developing web services and applications. In this blog post, we will explore how to create a simple RESTful web service using Kotlin and JetBrains tools. We’ll also provide a sample client code to demonstrate how to call the web service.

Prerequisites

Before we start, make sure you have the following prerequisites installed:

1. IntelliJ IDEA: Download and install the latest version of IntelliJ IDEA from JetBrains (https://www.jetbrains.com/idea/download/).
2. Kotlin Plugin: Install the Kotlin plugin in IntelliJ IDEA by going to Preferences/Settings > Plugins > Marketplace and search for „Kotlin.“

Creating the RESTful Web Service

Let’s create a basic RESTful web service that exposes a list of tasks. Follow these steps:

1. Create a New Project:
   • Open IntelliJ IDEA.
   • Click on „Create New Project.“
   • Choose „Kotlin“ as the project type.
   • Select the appropriate JDK version.
2. Create a Kotlin Class:
   • Right-click on the „src“ directory in your project.
   • Choose „New“ > „Kotlin File/Class.“
   • Name it „Task.kt.“
3. Define the Data Model:In the „Task.kt“ file, define a simple data class representing a task: data class Task(val id: Int, val title: String, val description: String)
4. Create a RESTful Controller:
   • Right-click on the „src“ directory again.
   • Choose „New“ > „Kotlin File/Class.“
   • Name it „TaskController.kt.“
   In „TaskController.kt,“ create a simple RESTful controller using Ktor, a lightweight web framework:

import io.ktor.application.*
import io.ktor.response.*
import io.ktor.routing.*
import io.ktor.server.engine.embeddedServer
import io.ktor.server.netty.Netty

fun Application.module() {
    routing {
        route("/tasks") {
            get {
                val tasks = listOf(
                    Task(1, "Task 1", "Description 1"),
                    Task(2, "Task 2", "Description 2")
                )
                call.respond(tasks)
            }
        }
    }
}

fun main() {
    embeddedServer(Netty, port = 8080, module = Application::module).start(wait = true)
}

This code defines a simple Ktor application that responds to GET requests at the „/tasks“ endpoint.

Creating a Sample Client

Now, let’s create a sample client to call the web service:

1. Create a Kotlin File for the Client:
   • Right-click on the „src“ directory.
   • Choose „New“ > „Kotlin File/Class.“
   • Name it „TaskClient.kt.“
2. Add Code to Make a GET Request:In „TaskClient.kt,“ add the following code to make a GET request to the web service.

import io.ktor.client.HttpClient
import io.ktor.client.engine.apache.Apache
import io.ktor.client.features.json.JsonFeature
import io.ktor.client.features.json.serializer.KotlinxSerializer
import io.ktor.client.request.get
import kotlinx.serialization.Serializable

@Serializable
data class Task(val id: Int, val title: String, val description: String)

suspend fun fetchTasks(): List<Task> {
    val client = HttpClient(Apache) {
        install(JsonFeature) {
            serializer = KotlinxSerializer()
        }
    }
    return client.get("http://localhost:8080/tasks")
}

suspend fun main() {
    val tasks = fetchTasks()
    for (task in tasks) {
        println("Task ${task.id}: ${task.title}")
    }
}

This code sets up an HTTP client using Ktor’s client library, makes a GET request to the „/tasks“ endpoint, and prints the tasks retrieved from the web service.

Running the Application

1. Run the web service by executing the main function in „TaskController.kt.“
2. Run the client application by executing the main function in „TaskClient.kt.“You should see the list of tasks displayed in the client’s console output.

Conclusion

In this blog post, we’ve learned how to create a simple RESTful web service using Kotlin and JetBrains tools like IntelliJ IDEA. We also provided a sample client code demonstrating how to call the web service. With Kotlin’s concise syntax and JetBrains‘ developer-friendly tools, you can easily develop robust web services for your projects.