How to Run Ktor Embedded Server from Code

Question

I've written a simple Ktor server that processes a JSON payload from an incoming POST request. Now, I want to spawn this server from another application, and after processing the request, shut it down.

So the first problem I need to solve is: how do I spawn the Ktor server from some other 'driver' Kotlin code? All the tutorials I've found online are 1-2 years old, and are apparently using an older version of Ktor, where the main class looks like this:

fun main(args: Array) {
    embeddedServer(Netty, 8080) {
        routing {
            get("/") {
                call.respondText("Hello from Kotlin Backend", ContentType.Text.Html)
            }
        }
    }.start(wait = true)
}

It's easy to see that one can just run the embeddedServer(Netty, 8080) { ... }.start(wait = true) from wherever they want, to spawn the server. But I downloaded the Ktor plugin for IntelliJ IDEA yesterday, and it seems things have changed lately. This is what the new main class looks like:

fun main(args: Array): Unit = io.ktor.server.netty.EngineMain.main(args)

@Suppress("unused") // Referenced in application.conf
@kotlin.jvm.JvmOverloads
fun Application.module(testing: Boolean = false) {
    install(ContentNegotiation) {
        gson {
        }
    }

    routing {
        get("/") {
            call.respondText("HELLO WORLD!", contentType = ContentType.Text.Plain)
        }

        get("/json/gson") {
            call.respond(mapOf("hello" to "world"))
        }
    }
}

Now, the Application.module(...) function takes care of setting up the routing and stuff, while the actual running of the server is done internally by io.ktor.server.netty.EngineMain.main(args). Also, properties like the port number are referenced from the application.conf file, and I'm not quite sure how it figures out where to find that application.conf file.

I have been able to run this Ktor server using gradlew. I also understand that it is possible to export it as an executable jar and run it (as explained here). But I can't find out how to run it from code. Any suggestions?

Edit: And it would be nice if I could set the port number from the driver code.

How to Run Ktor Embedded Server from Code

0 Answers