如何在scala中使用返回Future（Either [A，B]）的函数的返回值？

Question

我有以下功能。

def get(id: Int): Future[Either[String, Item]] = {
    request(RequestBuilding.Get(s"/log/$id")).flatMap { response =>
      response.status match {
        case OK => Unmarshal(response.entity).to[Item].map(Right(_))
        case BadRequest => Future.successful(Left(s"Bad Request"))
        case _ => Unmarshal(response.entity).to[String].flatMap { entity =>
          val error = s"Request failed with status code ${response.status} and entity $entity"
          Future.failed(new IOException(error))
        }
      }
    }
  }

我正在尝试调用此函数，但我不确定如何知道它返回的是字符串还是项。以下是我失败的尝试。

Client.get(1).onComplete { result =>
        result match {
          case Left(msg) => println(msg)
          case Right(item) => // Do something
        }
      }

Answer 1

onComplete 采用Try 类型的函数，因此您必须在Try 上进行双重匹配，并且在Either 成功的情况下

Client.get(1).onComplete {
  case Success(either) => either match {
    case Left(int) => int
    case Right(string) => string
  }
  case Failure(f) => f
}

虽然绘制未来要容易得多：

Client.get(1).map {
  case Left(msg) => println(msg)
  case Right(item) => // Do something
}

如果您想处理onComplete 的Failure 部分，请在映射未来后使用recover 或recoverWith。