Question

MyService.scala:33: could not find implicit value for parameter eh: spray.routing.ExceptionHandler

我在使用Akka时遇到了“缺少隐式”编译错误，在spray.io代码中，对一个单独的后端服务器进行http调用，作为响应http get的一部分。代码需要导入相当多的Spray和Akka库，所以有点难以确定是否存在导致这种情况的库冲突，我宁愿想出如何在这个和其他情况下逻辑地跟踪这类问题。

在调用runRoute(myRoute)

时遇到缺少的隐式

以下是代码：

import spray.routing._
import akka.actor.Actor
import akka.actor.ActorSystem
import spray.http._
import MediaTypes._
import akka.io.IO
import spray.httpx.RequestBuilding._
import scala.concurrent.Future
import spray.can.Http
import spray.http._
import akka.util.Timeout
import HttpMethods._
import akka.pattern.ask
import akka.event.Logging
import scala.concurrent.duration._


// we don't implement our route structure directly in the service actor because
// we want to be able to test it independently, without having to spin up an actor
class MyServiceActor extends Actor with MyService with akka.actor.ActorLogging {

  log.info("Starting")

  // the HttpService trait defines only one abstract member, which
  // connects the services environment to the enclosing actor or test
  def actorRefFactory = context

  // this actor only runs our route, but you could add
  // other things here, like request stream processing
  // or timeout handling
  def receive = runRoute(myRoute)
}

// this trait defines our service behavior independently from the service actor
trait MyService extends HttpService {

  implicit val system: ActorSystem = ActorSystem()

  implicit val timeout: Timeout = Timeout(15.seconds)

  import system.dispatcher // implicit execution context

  //val logger = context.actorSelection("/user/logger")
  val logger = actorRefFactory.actorSelection("../logger")

  val myRoute =
  {
    def forward(): String = {
      logger ! Log("forwarding to backend")  
      val response: Future[HttpResponse] =
      (IO(Http) ? Get("http:3080//localhost/backend")).mapTo[HttpResponse]    
      "<html><body><h1>api response after backend processing</h1></body></html>"
    }

    path("") {
      get {
        respondWithMediaType(`text/html`) { // XML is marshalled to `text/xml` by default, so we simply override here
          complete(forward)
        }
      }
    }
  }
}

我想知道解决这个问题的最佳方法是什么，希望能够提供有关如何解决类似问题的洞察力，因为它们在某种程度上并不能直接追踪。

编辑：当试图直接传递implicits，如下面的@ christian的答案，我得到：

MyService.scala:35: ambiguous implicit values: both value context in trait Actor of type => akka.actor.ActorContext and value system in trait MyService of type => akka.actor.ActorSystem match expected type akka.actor.ActorRefFactory RoutingSettings.default, LoggingContext.fromActorRefFactory) ^

不太确定为什么具体如@ christian的回答为编译器留下了歧义的空间......

Answer 1

我遇到了同样的“找不到参数eh：spray.routing.ExceptionHandler的隐含值”错误今天早些时候。我尝试了@Christian的方法，但看到一些“xxx的隐含价值”逐渐上升。在仔细检查错误消息后，我发现implicit val system = context.system向runRoute解决问题的演员添加了{{1}}。

Answer 2

runRoute期待一些暗示。您缺少导入：

import spray.routing.RejectionHandler.Default

<强>更新我认为我们也遇到了runRoute的一些问题，因为我们明确地提供了隐式参数：

runRoute(route)(ExceptionHandler.default, RejectionHandler.Default, context,
      RoutingSettings.default, LoggingContext.fromActorRefFactory)

<强> UPDATE2：要修复上一个错误，请删除ActorSystem的创建（在MyService中，您从MyServiceActor获取actor系统 - 因此您必须使用自我类型注释）。这编译：

import akka.actor.Actor
import akka.io.IO
import spray.httpx.RequestBuilding._
import spray.http.MediaTypes._
import spray.routing.{RoutingSettings, RejectionHandler, ExceptionHandler, HttpService}
import spray.util.LoggingContext
import scala.concurrent.Future
import spray.can.Http
import spray.http._
import akka.util.Timeout
import HttpMethods._
import akka.pattern.ask
import akka.event.Logging
import scala.concurrent.duration._


// we don't implement our route structure directly in the service actor because
// we want to be able to test it independently, without having to spin up an actor
class MyServiceActor extends Actor with MyService with akka.actor.ActorLogging {

  log.info("Starting")

  // the HttpService trait defines only one abstract member, which
  // connects the services environment to the enclosing actor or test
  implicit def actorRefFactory = context

  // this actor only runs our route, but you could add
  // other things here, like request stream processing
  // or timeout handling
  def receive = runRoute(myRoute)(ExceptionHandler.default, RejectionHandler.Default, context,
    RoutingSettings.default, LoggingContext.fromActorRefFactory)
}

// this trait defines our service behavior independently from the service actor
trait MyService extends HttpService { this: MyServiceActor =>

  implicit val timeout: Timeout = Timeout(15.seconds)

  implicit val system = context.system

  //val logger = context.actorSelection("/user/logger")
  val logger = actorRefFactory.actorSelection("../logger")

  val myRoute =
  {
    def forward(): String = {
      //logger ! Log("forwarding to backend")
      val response: Future[HttpResponse] =
        (IO(Http) ? Get("http:3080//localhost/backend")).mapTo[HttpResponse]
      "<html><body><h1>api response after backend processing</h1></body></html>"
    }

    path("") {
      get {
        respondWithMediaType(`text/html`) { // XML is marshalled to `text/xml` by default, so we simply override here
          complete(forward)
        }
      }
    }
  }
}

Spray / Akka缺少隐含

2 个答案: