Kotlin HTTP Requests with Ktor-Client — Android Studio Tutorial

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Ktor is a powerful Kotlin-based framework for building asynchronous servers, clients, and microservices. It offers a lightweight, yet comprehensive set of tools for building high-performance, scalable applications. In this tutorial, we’ll explore how to use Ktor’s client-side library, ktor-client, to make HTTP requests in an Android app.

Add the Ktor dependency to your project

To use ktor-client in your Android app, you need to add the following dependencies to your build.gradle file:

//Ktor client
implementation "io.ktor:ktor-client-core:1.6.4"
implementation "io.ktor:ktor-client-android:1.6.4"
implementation "io.ktor:ktor-client-json:1.6.4"
implementation "io.ktor:ktor-client-serialization:1.6.4"

Create a Ktor client instance

To make HTTP requests with ktor-client, you first need to create an instance of HttpClient. You can do this by calling the HttpClient constructor and passing in any optional configuration settings. Here I have installed and configured JsonFeature with KotlinxSerializer to automatically parse the JSON response into an object.

private val httpClient = HttpClient(Android) {
    install(JsonFeature) {
        serializer = KotlinxSerializer(kotlinx.serialization.json.Json {
            ignoreUnknownKeys = true
        })
    }
}

Create a data class for the response object

Create a data class to hold the response you’ll get from the API request. Here I am creating a data class for the response from the sample posts API.

@Serializable
data class Post(
    val userId: Int,
    val id: Int,
    val title: String,
    val body: String
)

Annotate the class with @Serializable annotation to use KotlinxSerializer.

Send a GET request

To send a GET request, you can use the get() function of the HttpClient instance and pass in the URL of the endpoint you want to hit.

val posts =
    httpClient.get<List<Post>> { url("https://jsonplaceholder.typicode.com/posts") }

This will send a GET request to the specified URL and return the response as a List of posts.

Handle errors

When making HTTP requests, it’s important to handle any potential errors that may occur. Ktor’s HttpClient throws exceptions for various types of errors, such as network timeouts or invalid requests. You can use a try-catch block to catch and handle these exceptions.

try {
    val posts =
        httpClient.get<List<Post>> { url("https://jsonplaceholder.typicode.com/posts") }
    recyclerView.layoutManager = LinearLayoutManager(this@MainActivity)
    recyclerView.adapter = PostAdapter(posts)
} catch (e: ClientRequestException) {
    Log.d(TAG, "ClientRequestException ${e.message}")
} catch (e: ServerResponseException) {
    Log.d(TAG, "ServerResponseException ${e.message}")
} catch (e: TimeoutException) {
    Log.d(TAG, "TimeoutException ${e.message}")
} catch (e: Exception) {
    Log.d(TAG, "Exception ${e.message}")
}

Close the client instance

Finally, when you’re done making HTTP requests, it’s important to close the HttpClient instance to free up any resources it may be using.

finally {
    httpClient.close()
}

This will release any network connections and other resources held by the client.

And that’s it! With these simple steps, you can use Ktor’s ktor-client library. You can find the complete code here.

Conclusion

In conclusion, Ktor-Client is a powerful tool for making HTTP requests in Android apps. It provides a simple and efficient way to handle network calls and supports various types of requests and responses. With the help of the code snippets provided in this tutorial, you can now integrate Ktor-Client into your own projects and make your app’s network interactions smoother and more reliable.