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Koin for Ktor

note

The koin-ktor project is updated for Ktor 2.0.1

The koin-ktor project is dedicated to bring dependency injection for Ktor.

Install Koin & inject​

To start a Koin container in Ktor, just install the Koin plugin like follow:

fun Application.main() {
    // Install Ktor features
    install(Koin) {
        slf4jLogger()
        modules(helloAppModule)
    }

}
note

You can also start it from outside of Ktor, but you won't be compatible with autoreload feature.

Injection in Application​

Koin inject() and get() functions are available from Application class:

fun Application.main() {
    //...

    // Lazy inject HelloService
    val service by inject<HelloService>()

    // Routing section
    routing {
        get("/hello") {
            call.respondText(service.sayHello())
        }
    }
}

Declaring Koin for a Ktor Module​

For a Ktor module, you can load specific Koin modules. Just declare them with koin { } function:

fun Application.module2() {
    koin {
        // load appModule2 for module2 Ktor module
        modules(appModule2)
    }

}

Injecting in Routing & Route​

Koin inject() and get() functions are available from Route & Routing classes:

fun Routing.v1() {

    // Lazy inject HelloService from within a Ktor Routing Node
    val service by inject<HelloService>()

    get("/v1/hello") {
        call.respondText("[/v1/hello] " + service.sayHello())
    }
}

From Route class:

fun Route.hello() {

    // Lazy inject HelloService from within a Ktor Route
    val service by inject<HelloService>()

    get("/v1/bye") {
        call.respondText("[/v1/bye] " + service.sayHello())
    }
}

Events​

You can listen to KTor Koin events:

fun Application.main() {
    // ...

    // Install Ktor features
    environment.monitor.subscribe(KoinApplicationStarted) {
        log.info("Koin started.")
    }

    environment.monitor.subscribe(KoinApplicationStopPreparing) {
        log.info("Koin stopping...")
    }

    environment.monitor.subscribe(KoinApplicationStopped) {
        log.info("Koin stopped.")
    }

    //...
}