akka-http and JSON

akka-http-json.md

JSON handling in akka-http.

Marshaller and Unmarshaller

• Marshalling
• Unmarshalling
• JSON Support (SprayJsonSupport by default)
• Marshalling & Unmarshalling (in routing DSL)

3rd parties

akka-http-json

Custom JSON (un)marshaller for akka-http by using 3rd party libraries. The community seems to be very active.

• hseeberger/akka-http-json

akka-http + Jackson

• takezoe/akka-http-jackson
  • JacksonSupport.scala

akka-http + circe

circe's decode[A] produces Either[Error, A] but akka-http requires Future[A]. _.fold(Future.failed, Future.successful) can be a solution to convert from Either[Throwable, A] to Future[A].

• CirceSupport.scala

Documents (in Japanese)

• [Akka-HTTP]spray-jsonの使い方とAkka-HTTP
• Akka-HTTPを型で縛る (Bind Akka-HTTP by types)
• Akka HTTPでJacksonを使ってJSON変換をする

UserClient.scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model.{HttpMethods, HttpRequest, StatusCodes, Uri}
import akka.http.scaladsl.unmarshalling.{FromEntityUnmarshaller, Unmarshal}
import akka.stream.ActorMaterializer
import de.heikoseeberger.akkahttpcirce.FailFastCirceSupport

import scala.concurrent.{ExecutionContext, Future}
import scala.util.{Failure, Success}

object UserService {

  case class User(id: Long, name: String, firstName: String, lastName: String, location: Location)
  
  case class Location(country: String, city: String)

}

trait UserServiceJsonSupport extends FailFastCirceSupport {

  import UserService._
  import io.circe.Decoder

  // enable automatic decoder derivation
  import io.circe.generic.auto._

  /**
    * ```
    * {
    *   "user": {
    *     "id": 1,
    *     "name": "okapies",
    *     "first_name": "Yuta",
    *     "last_name": "Okamoto",
    *     "location": {
    *       "country": "Japan",
    *       "city": "Tokyo"
    *     }
    *   }
    * }
    * ```
    */
  implicit val tokenInfoDecoder: Decoder[User] =
    Decoder.forProduct5("id", "name", "first_name", "last_name", "location")(User).prepare(_.downField("user"))
  // Note: The decoder for Location will be automatically derived by circe.

}

class UserServiceClient(val endpoint: Uri)
                       (implicit val system: ActorSystem,
                        val materializer: ActorMaterializer,
                        val executionContext: ExecutionContext) extends UserServiceJsonSupport {

  import UserService._

  def getUser(username: String): Future[User] =
    doRequest[User](HttpRequest(uri = Uri.parseAndResolve(s"/api/v1/users/$username", base = endpoint)))

  private[this] def doRequest[A: FromEntityUnmarshaller](request: HttpRequest): Future[A] =
    Http().singleRequest(request).transformWith {
      case Success(res) if res.status == StatusCodes.OK =>
        Unmarshal(res.entity).to[A]
      case Success(res) =>
        res.discardEntityBytes()
        Future.failed(new Exception(s"HttpRequest failed: $res"))
      case Failure(t) =>
        Future.failed(t)
    }

}