Kotlin is a statically typed programming language that runs on the Java Virtual Machine and also can be compiled to JavaScript source code. Kotlin is developed by JetBrains.
The Kotlin programming language has been gaining popularity lately due to its concise syntax and interoperability with Java. In this article, we're going to see how to use Kotlin to build and consume RESTful services.
Let's start by building a simple REST API with Kotlin. We're going to use the Ktor web framework to build our API.
First, we need to add the Ktor dependencies to our build.gradle
file:
dependencies {
implementation "io.ktor:ktor-server-core:1.3.2"
implementation "io.ktor:ktor-server-netty:1.3.2"
implementation "io.ktor:ktor-server-test:1.3.2"
}
Next, we can create a main.kt
file with the following code:
import io.ktor.application.*
import io.ktor.response.*
import io.ktor.routing.*
import io.ktor.server.engine.*
import io.ktor.server.netty.*
fun main(args: Array<String>) {
embeddedServer(Netty, 8080) {
routing {
get("/") {
call.respondText("Hello, World!")
}
}
}.start(wait = true)
}
In the code above, we're using the routing
DSL to define a route that responds with "Hello, World!" when the GET /
URL is accessed.
We can now run the application with the gradle run
command and access the http://localhost:8080
URL in our browser.
Now that we've seen how to build a REST API with Kotlin, let's see how to consume one. We're going to use the Retrofit library for this.
First, we need to add the Retrofit dependencies to our build.gradle
file:
dependencies {
implementation "com.squareup.retrofit2:retrofit:2.9.0"
implementation "com.squareup.retrofit2:converter-gson:2.9.0"
}
Next, we need to create a Service
interface that defines the methods we want to use to access the API:
interface Service {
@GET("/users/{id}")
fun getUser(@Path("id") id: Int): Call<User>
@POST("/users")
fun createUser(@Body user: User): Call<User>
@PUT("/users/{id}")
fun updateUser(@Path("id") id: Int, @Body user: User): Call<User>
@DELETE("/users/{id}")
fun deleteUser(@Path("id") id: Int): Call<Void>
}
In the code above, we're using the @GET
, @POST
, @PUT
, and @DELETE
annotations to define the methods we want to use to access the /users
URL.
We can now create a Retrofit
instance and use it to create a Service
instance:
val retrofit = Retrofit.Builder()
.baseUrl("https://api.example.com")
.addConverterFactory(GsonConverterFactory.create())
.build()
val service = retrofit.create(Service::class.java)
We can now use the service
object to access the API. For example, we can use the getUser
method to retrieve a user with id = 1
:
val user = service.getUser(1).execute().body()
In this article, we've seen how to use Kotlin to build and consume RESTful services. Kotlin is a concise and interoperable language that is gaining popularity due to its many benefits.