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我正在试验 Akka 流和 twitter4j-stream。拥有一系列推文它可以正常工作，直到它失败的那一刻NPE，这对我来说没有意义。

最初我正在创建一个client：

val client: TwitterStream = {
  using(TwitterClient.clientFactory.getInstance()) { inst =>
    inst.setOAuthConsumer(auth.consumerKey, auth.consumerSecret)
    inst.setOAuthAccessToken(new AccessToken(auth.accessTokenKey, auth.accessTokenSecret))
  }
}

最后，我想得到具有以下签名的东西：val stream: Source[TwitterEvent, ShutdownHandler]所以我正在创建一个 ReactiveStreams Publisher，它将Source使用来自客户端的使用：

val pub = new Publisher[TwitterEvent] {
  override def subscribe(s: Subscriber[_ >: TwitterEvent]): Unit = {
    client.addListener(new TwitterListener(s))
    client.filter(filter)
  }
}

val stream: Source[TwitterEvent, ShutdownHandler] = {
  Source.fromPublisher(pub).mapMaterializedValue { nu =>
    new TwitterClient.ShutdownHandler(() => client.shutdown())
  }
}

所以.filter()引导这个东西，我收到了一些推文，然后它失败了：

[ERROR] [04/08/2016 15:18:19.301] [System-akka.actor.default-dispatcher-4] [akka://System/user/StreamSupervisor-0/flow-0-0-foreachSink-foreachSink-map] It is illegal to throw exceptions from request(), rule 3.16
akka.stream.impl.ReactiveStreamsCompliance$SignalThrewException: It is illegal to throw exceptions from request(), rule 3.16
    at akka.stream.impl.ReactiveStreamsCompliance$.tryRequest(ReactiveStreamsCompliance.scala:111)
...
Caused by: java.lang.NullPointerException
    at akka.stream.impl.ReactiveStreamsCompliance$.tryRequest(ReactiveStreamsCompliance.scala:110)

如果这很重要，我的TwitterListener：

final class TwitterListener(s: Subscriber[_ >: TwitterEvent]) extends StatusAdapter {
    override def onStatus(status: Status): Unit = {
      if (status != null) {
        val message = new TwitterEvent(status)
        s.onNext(message)
      }
    }

    override def onException(ex: Exception): Unit = {
      s.onError(ex)
    }
  }
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