This example shows how we can expose REST Akka Http end point using Source Streaming

RestSourceStream.scala

import akka.NotUsed
import akka.http.scaladsl.common.{EntityStreamingSupport, JsonEntityStreamingSupport}
import akka.http.scaladsl.marshallers.sprayjson.SprayJsonSupport
import akka.http.scaladsl.model.headers.Accept
import akka.http.scaladsl.model.{MediaRange, MediaTypes}
import akka.http.scaladsl.server.{Directives, Route}
import akka.http.scaladsl.testkit.ScalatestRouteTest
import akka.stream.scaladsl.Source
import org.scalatest.{Matchers, WordSpec, WordSpecLike}
import spray.json.DefaultJsonProtocol


/**
  * Created by arun sethia on 5/21/18.
  */
class RestSourceStream extends WordSpec with WordSpecLike
  with Matchers
  with ScalatestRouteTest
  with Directives with DefaultJsonProtocol
  with SprayJsonSupport {

  implicit val jsonStreamingSupport: JsonEntityStreamingSupport = EntityStreamingSupport.json()

  val AcceptJson = Accept(MediaRange(MediaTypes.`application/json`))
  val AcceptXml = Accept(MediaRange(MediaTypes.`text/xml`))

  case class Tweet(uid: Int, txt: String)

  case class Measurement(id: String, value: Int)

  implicit val tweetFormat = jsonFormat2(Tweet.apply)
  implicit val measurementFormat = jsonFormat2(Measurement.apply)

  val route: Route =
    path("tweets" / Segment) { n =>
      // [3] simply complete a request with a source of tweets:
      val tweets: Source[Tweet, NotUsed] = Source.repeat[Tweet](Tweet(12, "Hello World!")).take(n.toInt)
      complete(tweets)
    }


  "tweet" should {
    "get 10 tweets" in {
      Get("/tweets/10").withHeaders(AcceptJson) ~> route ~> check {
        assert(responseAs[List[Tweet]].length==10)
      }
    }
    "get 20 tweets" in {
      Get("/tweets/20").withHeaders(AcceptJson) ~> route ~> check {
        assert(responseAs[List[Tweet]].length==20)
      }
    }
  }
}