with custom directive

akkahttpmarshaller.scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.marshalling.{Marshaller, PredefinedToEntityMarshallers, ToEntityMarshaller}
import akka.http.scaladsl.model.headers.RawHeader
import akka.http.scaladsl.model.{HttpRequest, MediaTypes}
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
import de.heikoseeberger.akkahttpjson4s.Json4sSupport
import org.json4s
import org.json4s.DefaultFormats

import scala.io.StdIn

sealed trait MyType {
  val body: String
}

case class SomeClass(body: String) extends MyType

object WebServer  {

  def main(args: Array[String]) {

    implicit val serialization = json4s.jackson.Serialization // or native.Serialization
    implicit val formats = DefaultFormats

    implicit val system = ActorSystem("my-system")
    implicit val materializer = ActorMaterializer()
    // needed for the future flatMap/onComplete in the end
    implicit val executionContext = system.dispatcher

    def plainText[A <: MyType]: ToEntityMarshaller[A] = {
      PredefinedToEntityMarshallers.stringMarshaller(MediaTypes.`text/plain`).compose(_.body)
    }

    def json[A <: MyType]: ToEntityMarshaller[A] = {
      PredefinedToEntityMarshallers.stringMarshaller(MediaTypes.`application/json`).compose(serialization.write(_))
    }

    implicit def marshaller[A <: MyType]: ToEntityMarshaller[A] =
      Marshaller.oneOf(plainText, json)

    def transformToPlainTextRequest(req: HttpRequest): HttpRequest =
      req.uri.query().get("raw") match {
        case None => req
        case Some("true") =>  req.copy(headers =
          req.headers.filter(_.name() != "Accept") :+ RawHeader("Accept", "text/plain"))
        case Some("false") | _ => req
      }

    val supportRawRequest = mapRequest(transformToPlainTextRequest)

    val route =
      path("hello") {
        get {
          supportRawRequest {
            complete {
              SomeClass("hello")
            }
          }
        }
      }

    val bindingFuture = Http().bindAndHandle(route, "localhost", 8080)

    println(s"Server online at http://localhost:8080/\nPress RETURN to stop...")
    StdIn.readLine() // let it run until user presses return
    bindingFuture
      .flatMap(_.unbind()) // trigger unbinding from the port
      .onComplete(_ => system.terminate()) // and shutdown when done
  }
}