Akka-Java 在 ask-await 上抛出 DeadLetterException答案

【问题标题】：Akka-Java is throwing DeadLetterException on ask-awaitAkka-Java 在 ask-await 上抛出 DeadLetterException
【发布时间】：2016-09-08 04:16:08
【问题描述】：

我在这样的文件中有一个驱动程序/主类。（基本上我正在尝试混合 STORM 和 AKKA）。在 TenderEventSpout2 类中，我正在尝试向/从演员发送和接收消息。

public class TenderEventSpout2 extends BaseRichSpout {  
        ActorSystemHandle actorSystemHandle;
        ActorSystem _system;
        ActorRef eventSpoutActor;
        Future<Object> future;
        Timeout timeout;
        String result;

    @Override
    public void open(Map map, TopologyContext topologyContext, SpoutOutputCollector spoutOutputCollector) {
        //String[] message = {"WATCH_DIR"};
        timeout = new Timeout(Duration.create(60, "seconds"));
        List<Object> messageList = new ArrayList<Object>(); 

        messageList.add("WATCH_DIR");

        messageList.add(this.inputDirName);

        actorSystemHandle = new ActorSystemHandle();
        _system = actorSystemHandle.getActorSystem();
        eventSpoutActor = _system.actorOf(Props.create(EventSpoutActor.class));


        future = Patterns.ask(eventSpoutActor, messageList, timeout);

    }

    @Override
    public void nextTuple() {
        String result = null;
        try{
            result = (String) Await.result(future, timeout.duration());
        }
        catch(Exception e){
            e.printStackTrace();
        }
}

我的演员是：

public class EventSpoutActor extends UntypedActor {
public ConcurrentLinkedQueue<String> eventQueue = new ConcurrentLinkedQueue<>();
Inbox inbox;
@Override 
public void onReceive(Object message){// throws IOException {
    if (message instanceof List<?>) {
        System.out.println(((List<Object>)message).get(0)+"*******************");
        if(((List<Object>)message).get(0).equals("WATCH_DIR")){
            final List<Object> msg = (List<Object>)message;
            Thread fileWatcher = new Thread(new Runnable(){

                @Override
                public void run() {

                        System.out.println(msg.get(1)+"*******************");
                        try {

                            String result = "Hello";
                            System.out.println("Before Sending Message *******************");
                            getSender().tell(result, getSelf());
                            } 
                        catch (Exception e) {
                            getSender().tell(new akka.actor.Status.Failure(e), getSelf());
                            throw e;
                            }

                }
            });
            fileWatcher.setDaemon(true);
            fileWatcher.start();
            System.out.println("Started file watcher");
        }
    } 
    else{
        System.out.println("Unhandled !!");
        unhandled(message);
    }
}

}

我可以向我的 EventSpoutActor 发送消息。但面临接收消息的问题。这是为什么？？我在控制台中打印以下消息：

[EventProcessorActorSystem-akka.actor.default-dispatcher-3]
[akka://EventProcessorActorSystem/deadLetters] Message [java.lang.String]      
from Actor[akka://EventProcessorActorSystem/user/$a#-1284357486] to  
Actor[akka://EventProcessorActorSystem/deadLetters] was not delivered. [1] 
dead letters encountered.
This logging can be turned off or adjusted with configuration settings 
'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

【问题讨论】：

标签： java akka future dead-letter

【解决方案1】：

所以，我发现了邮件未送达的原因。

 getSender().tell(result, getSelf());

本应将消息发送给发送者的这一行在线程代码中使用时丢失了它的上下文数据：

 Thread fileWatcher = new Thread(new Runnable(){

            @Override
            public void run() {

                    System.out.println(msg.get(1)+"*******************");
                    try {

                        String result = "Hello";
                        System.out.println("Before Sending Message *******************");
                        getSender().tell(result, getSelf());

当我将“tell”代码移到线程外时，它起作用了。

【讨论】：