Play 2.4 WebSocket 在使用编译时依赖注入时抛出 InstantiationException

Question

Play 2.4 中的 WebSockets 在使用编译时依赖注入时似乎不起作用。我使用的是最新版本 2.4.2。具体来说，它在连接时抛出以下异常：

play.api.http.HttpErrorHandlerExceptions$$anon: Execution exception[[InstantiationException: null]]
    at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:254) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler.scala:180) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$messageReceived.applyOrElse(PlayDefaultUpstreamHandler.scala:182) [play-netty-server_2.11-2.4.0.jar:2.4.0]
    at play.core.server.netty.PlayDefaultUpstreamHandler$$anonfun$messageReceived.applyOrElse(PlayDefaultUpstreamHandler.scala:180) [play-netty-server_2.11-2.4.0.jar:2.4.0]
    at scala.runtime.AbstractPartialFunction.apply(AbstractPartialFunction.scala:36) [scala-library-2.11.6.jar:na]
    at scala.util.Failure$$anonfun$recover.apply(Try.scala:215) [scala-library-2.11.6.jar:na]
    at scala.util.Try$.apply(Try.scala:191) [scala-library-2.11.6.jar:na]
    at scala.util.Failure.recover(Try.scala:215) [scala-library-2.11.6.jar:na]
    at scala.concurrent.Future$$anonfun$recover.apply(Future.scala:324) [scala-library-2.11.6.jar:na]
    at scala.concurrent.Future$$anonfun$recover.apply(Future.scala:324) [scala-library-2.11.6.jar:na]
    at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:32) [scala-library-2.11.6.jar:na]
    ...
Caused by: java.lang.InstantiationException: null
    at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:48) ~[na:1.8.0_45]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422) ~[na:1.8.0_45]
    at java.lang.Class.newInstance(Class.java:442) ~[na:1.8.0_45]
    at play.api.inject.NewInstanceInjector$.instanceOf(Injector.scala:49) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.api.inject.SimpleInjector$$anonfun$instanceOf.apply(Injector.scala:85) ~[play_2.11-2.4.0.jar:2.4.0]
    at scala.collection.MapLike$class.getOrElse(MapLike.scala:128) ~[scala-library-2.11.6.jar:na]
    at scala.collection.AbstractMap.getOrElse(Map.scala:59) ~[scala-library-2.11.6.jar:na]
    at play.api.inject.SimpleInjector.instanceOf(Injector.scala:85) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.api.inject.SimpleInjector.instanceOf(Injector.scala:80) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.api.Application$$anonfun$instanceCache.apply(Application.scala:234) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.api.Application$$anonfun$instanceCache.apply(Application.scala:234) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.utils.InlineCache.fresh(InlineCache.scala:69) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.utils.InlineCache.apply(InlineCache.scala:62) ~[play_2.11-2.4.0.jar:2.4.0]
    at play.api.libs.concurrent.Akka$.system(Akka.scala:37) ~[play_2.11-2.4.0.jar:2.4.0]
    ...

控制器的外观如下：

class Application extends Controller {
  import play.api.Play.current
  def socket = WebSocket.acceptWithActor[String, String] { request => out =>
    WebSocketActor.props(out)
  }
}

object WebSocketActor {
  def props(out: ActorRef) = Props(new WebSocketActor(out))
}

class WebSocketActor(out: ActorRef) extends Actor {
  def receive = {
    case msg: String =>
      out ! ("Received message: " + msg)
  }
}

下面是 ApplicationLoader 的样子：

class AppLoader extends ApplicationLoader {
  override def load(context: Context): Application = new AppComponents(context).application
}

class AppComponents(context: Context) extends BuiltInComponentsFromContext(context) {
  lazy val appController = new controllers.Application
  lazy val router = new Routes(httpErrorHandler, appController, assets)
  lazy val assets = new controllers.Assets(httpErrorHandler)
}

Answer 1

原来这是 Play 2.4.2 中的错误。目前有一个 pull request 可以修复它。

在它被修复之前，我通过覆盖 AppComponents 的 injector 来解决它，同时也包括 actorSystem。所以 AppComponents 变成：

class AppComponents(context: Context) extends BuiltInComponentsFromContext(context) {
  lazy val appController = new controllers.Application
  lazy val router = new Routes(httpErrorHandler, appController, assets)
  lazy val assets = new controllers.Assets(httpErrorHandler)

  // temporary workaround until issue #4614 in playframework is fixed. See https://github.com/playframework/playframework/issues/4614
  override lazy val injector = new SimpleInjector(NewInstanceInjector) + router.asInstanceOf[play.api.routing.Router] + crypto + httpConfiguration + actorSystem
}

Play 2.4 WebSocket 在使用编译时依赖注入时抛出 InstantiationException

Play 2.4 WebSocket throws InstantiationException when using compile-time dependency injection

scala

websocket

playframework-2.4