3 Replies Latest reply on Mar 19, 2010 9:21 AM by Nick Belaevski

    a4j push - bind to jms topic

    Michal Glowacki Novice

      hi,

       

         I have read that it is possible to connect a4j push component to jms. I try to make a messaging system for customers - when one producer publishes the message, all logged in customers should get this message throught a4j:push component.

       

      Assuming my MDB works fine, here's the code snippet for my class used by a4j:push:

       

      @Name("alertsPush")

      public class AlertsPush implements javax.jms.MessageListener, Serializable {

      /**

      *

      */

      private static final long serialVersionUID = -7549165554107841679L;

       

      @Logger

      private Log log;

       

      PushEventListener listener;

      private long lastAlertTimestamp;

      private ArrayList<AlertModel> alertsList;

       

      public AlertsPush() throws Exception {

      Hashtable env = new Hashtable();

              env.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");

              env.put(Context.PROVIDER_URL, "jnp://localhost:1099");

              env.put(Context.URL_PKG_PREFIXES, "org.jboss.naming:org.jnp.interfaces");

              env.put(Context.SECURITY_AUTHENTICATION, "none");

              Context context = new InitialContext(env);      

       

      TopicConnectionFactory factory = (TopicConnectionFactory)

              context.lookup("ConnectionFactory");  

          Topic topic = (Topic)context.lookup("topic/Alerts");

          TopicConnection connect = factory.createTopicConnection();

          TopicSession session =

              connect.createTopicSession(false,Session.AUTO_ACKNOWLEDGE);

          TopicSubscriber subscriber = session.createSubscriber(topic);

          subscriber.setMessageListener(this);   

          connect.start();

      }

       

      public void addListener(EventListener listener) {

      synchronized (listener) {

      if (this.listener != listener) {

      this.listener = (PushEventListener) listener;

      }

      }

      }

       

      public void onMessage(Message arg0) {

      log.error("ALERT RECEIVED");

      try {

      updateAlertsList();

      } catch (Exception e) {

      // TODO Auto-generated catch block

      e.printStackTrace();

      }

      listener.onEvent(new EventObject(this));

      }

       

      private void updateAlertsList() throws Exception {

      AlertsCache cache = AlertsCache.getInstance();

      this.alertsList = cache.getAlerts();

      }

       

      public void setAlertsList(ArrayList<AlertModel> alertsList) {

      this.alertsList = alertsList;

      }

       

      public ArrayList<AlertModel> getAlertsList() {

      return alertsList;

      }

       

       

      }

       

       

      And XHMTL code for this component is as follows:

       

      <a4j:push interval="5000" eventProducer="#{alertsPush.addListener}" reRender="alertsTable" enabled="true" id="alertsPush"/>

       

      unfortunaly the line:

       

      listener.onEvent(new EventObject(this));

       

      throws RuntimeException (NullPointerException) when I publish an alert. I don't know how to register listener when I want to use Message Driven Bean (topic). Anyone could give me a hint?