jms pub sub

[Pinda Ros]

Hello, I have developed and JMS EJB with a publisher and subscriber.
My question is when i send a message to the message driven bean which is deployed in jboss app/server through the publisher, is it important which client starts first, that is subscriber or producer?
Any references to jms and mdbs will be highly appreciated.
Thank you in advance.
pinda

[eammon bannon]

It doesn't matter what "starts first" - since you are not sending a message directly from one MDB to another, you send a message to a topic. A message consumer subscribes to a topic, and listens for messages to arrive on it. Its a completely asynchronous process, so nothing is required of the consuming MDB by the producing MDB. Depending on your persistance strategy you could ever stop the server and the message will still reach your consumer.

[Pinda Ros]

Hello and thank you for your answer,
Do you know if it is necessary to have a message listener?
pinda

[eammon bannon]

No, nothing inthe publisher requires this. But it would be silly not to - otherwise your just gradually filling a topic up with useless messages.

[Pinda Ros]

So what exactly is the usage of the message listener?
Is the subscriber using the message listener, when a message is published, to receive the message and remove it from the topic.
Will the subscriber be able to receive another message from a publisher on the same topic.
At the moment i have developed an mdb,publisher and subscriber and i receive only the first message without any listener whatsoever.
However if i add the following line: subscriber.setMessageListener(this); i get the following exception: javax.jms.JMSException: A message listener is already registered. My class implements MessageListener and onMessage method.
Any ideas?
Thank you in advance.
pinda

[Pinda Ros]

Problem solved, i attach the files for future reference to others...
mdb for non-durable messages
subscriber

 
import java.io.*;
import javax.jms.*;
import javax.naming.*;
import java.util.*;
import javax.swing.*;

public class JMSPubSubReceive implements MessageListener{    
  private TopicSession pubSession;
  private TopicSession subSession;  
  private TopicSubscriber subscriber;
  public TopicConnection connection;
  private String username;  
  
  //default constructor
  public JMSPubSubReceive()throws Exception{
    // Context is loaded from the jndi.properties for the spefici vendor
    Hashtable env = new Hashtable();
    env.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");
    env.put(Context.PROVIDER_URL,"jnp://dstepc:1099");
    Context context = new InitialContext(env);
    
    TopicConnectionFactory topicFactory = (TopicConnectionFactory) context.lookup("java:/ConnectionFactory");
    //create a jms connection
    connection = topicFactory.createTopicConnection();
    System.out.println("JMS Connection created");
    
    //create a session            
    TopicSession subSession = connection.createTopicSession(false,Session.AUTO_ACKNOWLEDGE);
    System.out.println("Session created");
    //lookup a spefici jms topic   
    Topic topic = (Topic) context.lookup("topic/MDB");    
    System.out.println("Topic found");
    
    //create a jms subscriber
    subscriber = subSession.createSubscriber(topic);    
    System.out.println("Subscriber created");
    
    //set a jms message listerner
    subscriber.setMessageListener(this);     
    System.out.println("Listener registered");
    
    //initialize the chat application
    set(connection, subSession, subscriber);    
    //start the jms connection; allows the messages to be delivered
    connection.start();
    
  }//end of constructor
   
  public void set(TopicConnection con, TopicSession subSess, TopicSubscriber sub){
    this.connection = con;    
    this.subSession =subSess;
    this.subscriber = sub;
  }//end of set method
  
  void doThread(String text)
  {
   System.out.println("mesa sto doThread");  
 
  }
  //Receive message from topic subscriber
  public void onMessage(Message message){
    try{
      TextMessage textMessage = (TextMessage)message;
      String text= textMessage.getText();
      //JOptionPane.showMessageDialog(null,);
      System.out.println("before check");
      if (text.equals("update"))
      {
        System.out.println(text);
        JOptionPane.showMessageDialog(null,text,text,JOptionPane.INFORMATION_MESSAGE); 
       }
      else
      {
      System.out.println(text);  
      }
    }
    catch(JMSException ex){
      ex.printStackTrace();
    }
  }//end of method
  
  
  //close the jms connection
  public void close()throws JMSException{
    connection.close();
  }//end of method
   
    public static void main(String[] args) throws Exception{
    
      try{
        JMSPubSubReceive receiver = new JMSPubSubReceive();        
      }
      catch(Exception ex){
        ex.printStackTrace();
      }
    }//end of main
     
}
 

publisher

  
import javax.naming.*;
import javax.jms.*;
import java.util.*;
public class Client {
 public static void main (String[] args) throws Exception {
    // Initialize JNDI
 
    Hashtable env = new Hashtable();
    env.put(Context.INITIAL_CONTEXT_FACTORY, "org.jnp.interfaces.NamingContextFactory");
    env.put(Context.PROVIDER_URL,"jnp://dstepc:1099");
    Context ctx = new InitialContext(env);    
  
    // 1: Lookup ConnectionFactory via JNDI
    TopicConnectionFactory factory = (TopicConnectionFactory)ctx.lookup("java:/ConnectionFactory");
    // 2: Use ConnectionFactory to create JMS connection
    TopicConnection connection =  factory.createTopicConnection();  
    // 3: Use Connection to create session
    TopicSession session = connection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);
    // 4: Lookup Desintation (topic) via JNDI
    Topic topic = (Topic) ctx.lookup("topic/MDB");    
    // 5: Create a Message Producer
    TopicPublisher publisher = session.createPublisher(topic);    
   // 6: Create a text message, and publish it
    TextMessage msg = session.createTextMessage();
    for (int i=0;i<2;i++){
    msg.setText("2");
    System.out.println("2");
    publisher.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
    publisher.publish(msg);
    Thread.sleep(1000);
    }
     msg.setText("update");
    publisher.publish(msg);
    System.out.println("update1");
  
    System.out.println("update2");
    publisher.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
    
 }
 
}