README.md

Dropwizard Kotlin

This bundle integrates various components of the kotlin ecosystem with Dropwizard to better facilitate the use of Kotlin as the native language in which to build applications and components.

To use this bundle, add it to your application in the initialize method:

@Override
public void initialize(Bootstrap<T> bootstrap) {
    bootstrap.addBundle(new KotlinBundle<>());
}

Coroutines

Coroutines can easily be executed both at the application level and at the request level with structured concurrency semantics.

Application Scope

A CoroutineScope is made available at the container level for tracking background operations and ensuring a timely and clean shutdown. This can be injected into any class and used to launch coroutines in place of GlobalScope:

class Test @Inject constructor(
    @Named(ApplicationCoroutineScope.NAME)
    private val appScope: CoroutineScope
) : ApplicationEventListener {
    override fun onEvent(event: ApplicationEvent) {
        if (event.type == INITIALIZATION_START) {
            appScope.launch {
                delay(10_000)
                println("It's been 10 seconds since the application initialized!")
            }
        }
    }

    override fun onRequest(requestEvent: RequestEvent): RequestEventListener? = null
}

environment.jersey().register(Test::class.java)

To access this scope, inject a parameter of type CoroutineScope and qualified by the name ApplicationCoroutineScope.NAME into any component. This scope will be active until the application is either reloaded or destroyed, and upon application shutdown will be cancelled to notify all active children of pending shutdown.

Request Scope

Coroutines are natively supported as resource handlers. Jersey resource methods with the suspend modifier will automatically be detected and executed in a suspending request context, freeing up request threads to handle other requests when the handlers block:

class MyResource {

    @GET
    @Path("/wakeup")
    suspend fun lazyHelloWorld(): String {
        delay(10_000)
        return "Eh... is the sun up yet?"
    }
}

MDC

THe SLF4J MDC should be properly preserved from the request filters through the coroutine and the response filters.

Dispatching

Resource coroutines are dispatched using the Jetty thread pool, providing simplified thread management for the application. This behavior can be overridden by binding a custom dispatcher to CoroutineDispatcher in Jersey/HK2, though keep in mind that it will need to be safe for blocking since Jersey writes responses in a blocking manner.

Jackson Serialization

Support for serializing and deserializing kotlin types with the built-in Jackson ObjectMapper is enabled, allowing the use of kotlin types in configuration and request/response payloads.