Question

public class QueueListener implements MessageListener {

    public static final ExecutorService executor = Executors.newWorkStealingPool();

    public static boolean isActorinit=false;
    public static ActorSystem system=null;
    private ActorRef myActor=null;
    private String _queueName=null; 

    public QueueListener(String qName){
        this._queueName = qName;
        if(!isActorinit){
            system=ActorSystem.create("Controller");

            try {
            myActor=system.actorOf(Props.create(MessageExecutor.class.getConstructor(String.class).newInstance(_queueName).getClass()),"mysysActor");
            } catch (Exception e) {
                // TODO Auto-generated catch block
            }
            isActorinit=true;
        }
    }

    /* 
     * (non-Javadoc)
     * @see javax.jms.MessageListener#onMessage(javax.jms.Message)
     */
    @Override
    public void onMessage(Message msg) {

//      processRequest(msg);
        executeRequest(msg);
    }

    /** This method will process the message fetch by the listener.
     *   
     * @param msg - javax.jms.Messages parameter get queue message
     */
    private void processRequest(Message msg){

        String requestData=null;
        try {

            if(msg instanceof TextMessage){
                TextMessage textMessage= (TextMessage) msg;
                requestData = textMessage.getText().toString();
            }else if(msg instanceof ObjectMessage){
                ObjectMessage objMsg = (ObjectMessage) msg; 
                requestData = objMsg.getObject().toString();
            }


            MessageProcessor msgProcessor = new MessageProcessor(_queueName, requestData);
            executor.submit(msgProcessor);
        } catch (JMSException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

    }

    private void executeRequest(Message msg){

        String requestData=null;
        try {

            if(msg instanceof TextMessage){
                TextMessage textMessage= (TextMessage) msg;
                requestData = textMessage.getText().toString();
            }else if(msg instanceof ObjectMessage){
                ObjectMessage objMsg = (ObjectMessage) msg; 
                requestData = objMsg.getObject().toString();
            }
//           MessageExecutor objMessageExecutor=new MessageExecutor(_queueName);
            myActor.tell(requestData, ActorRef.noSender()); 

        } catch (JMSException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

    }

}

使用ExecutorService执行ProcessRequst方法时，此代码工作正常。然而，面对akka actor系统实现的问题。

Exception in thread "Thread-4" java.lang.NullPointerException
    at com.syn.jms.listener.QueueListener.executeRequest(QueueListener.java:102)
    at com.syn.jms.listener.QueueListener.onMessage(QueueListener.java:59)
    at org.apache.qpid.amqp_1_0.jms.impl.SessionImpl$Dispatcher.run(SessionImpl.java:942)
    at java.lang.Thread.run(Thread.java:745)

请注意我使用Apache qpid APi与activeMQ进行AMQP协议。

我无法理解这个问题。

Answer 1

我找到了解决方案，这是由于Actor ref的NPE，同时处理多个输入，每个进程队列都有唯一的actorRef，而且它没有初始化对象。我找到了这个解决方案。

public QueueListener(String actorId,String qName){
        this._queueName = qName;
         if(!isActorinit){
                system=ActorSystem.create(actorId);

                isActorinit=true;
            }

          myActor=system.actorOf( Props.create(MessageExecutor.class, qName),qName);
    }

然而，我建议您接触我的解决方案。 Thnaks

Answer 2

创建actor需要很少的时间，在创建actor期间，如果你收到消息进行处理，你将获得空指针异常。

在向其发送消息之前，您可能需要检查'myActor'是否为null。或者您可以考虑使用actor生命周期事件来开始处理消息。

带有akka和多线程的JMS

2 个答案: