def completeWith[T](marshaller: ToResponseMarshaller[T])(inner: (T => Unit) => Unit): Route


Uses the marshaller for a given type to produce a completion function that is passed to its inner route. You can use it to decouple marshaller resolution from request completion.

The completeWith directive works in conjunction with the instanceOf directive to convert higher-level (object) structure into some lower-level serialized “wire format”. The marshalling documentation explains this process in detail. This directive simplifies exposing types to clients via a route while providing some form of access to the current context.

completeWith is similar to handleWith. The main difference is with completeWith you must eventually call the completion function generated by completeWith. handleWith will automatically call complete when the handleWith function returns.


The following example uses spray-jsonJson Support via Jackson to marshall a simple Person class to a json response. It utilizes SprayJsonSupport via the PersonJsonSupport object as the in-scope unmarshaller.

sourceimport spray.json.{ DefaultJsonProtocol, RootJsonFormat }

object PersonJsonSupport extends DefaultJsonProtocol with SprayJsonSupport {
  implicit val personFormat: RootJsonFormat[Person] = jsonFormat2(Person.apply)
case class Person(name: String, favoriteNumber: Int)
sourcestatic public class Person {
  private final String name;
  private final int favoriteNumber;

  //default constructor required for Jackson
  public Person() { = "";
    this.favoriteNumber = 0;

  public Person(String name, int favoriteNumber) { = name;
    this.favoriteNumber = favoriteNumber;

  public String getName() {
    return name;

  public int getFavoriteNumber() {
    return favoriteNumber;

The findPerson takes an argument of type Person => UnitConsumer<Consumer<Person>> which is generated by the completeWith call. We can handle any logic we want in findPerson and call our completion function to complete the request.

sourceimport PersonJsonSupport._

val findPerson = (f: Person => Unit) => {

  //... some processing logic...

  //complete the request
  f(Person("Jane", 42))

val route = get {
  completeWith(instanceOf[Person]) { completionFunction => findPerson(completionFunction) }

// tests:
Get("/") ~> route ~> check {
  mediaType shouldEqual `application/json`
  responseAs[String] should include(""""name":"Jane"""")
  responseAs[String] should include(""""favoriteNumber":42""")
sourceimport static akka.http.javadsl.server.Directives.completeWith;

final Marshaller<Person, HttpResponse> marshaller = Marshaller.entityToOKResponse(Jackson.<Person>marshaller());

//Please note that you can also pass completionFunction to another thread and use it there to complete the request.
//For example:
//final Consumer<Consumer<Person>> findPerson = completionFunction -> {
//  CompletableFuture.runAsync(() ->
//   /* ... some processing logic... */
//   completionFunction.accept(new Person("Jane", 42)));
final Consumer<Consumer<Person>> findPerson = completionFunction -> {

  //... some processing logic...

  //complete the request
  completionFunction.accept(new Person("Jane", 42));

final Route route = completeWith(marshaller, findPerson);

// tests:
final TestRouteResult routeResult = testRoute(route).run(
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