Static Message Selector Example

This example shows you how to configure a JMS queue with static message selectors (filters).

Static message selectors are ActiveMQ's extension to message selectors as defined in JMS spec 1.1. Rather than specifying the selector in the application code, static message selectors are defined in one of ActiveMQ's configuration files, activemq-jms.xml, as an element called 'selector' inside each JMS queue definition:

      	<queue name="selectorQueue">
            <entry name="/queue/selectorQueue">
      	    <selector string="color='red'"/>
      	</queue>
     

Once configured the queue selectorQueue only delivers messages that are that match the selector; i.e. only the messages whose color property is equal to 'red' can be received by its consumers. Those that don't match the selector will be dropped by the queue and therefore will never be delivered to any of its consumers.

In the example code, five messages with different color property values are sent to queue selectorQueue. One consumer is created to receive messages from the queue. Of the five sent messages, two have a color property set to 'red', one has it set to 'blue', another to 'green', and one has not the color property at all. The result is that the consumer only gets the two messages with the 'red' color.

Example step-by-step

To run the example, simply type mvn verify from this directory

1. First we need to get an initial context so we can look-up the JMS connection factory and destination objects from JNDI. This initial context will get it's properties from the client-jndi.properties file in the directory ../common/config

           InitialContext initialContext = getContext();
        

2. We look-up the JMS queue object from JNDI, this is the queue that has the selector configured with it.

           Queue queue = (Queue) initialContext.lookup("/queue/selectorQueue");
        

3. We look-up the JMS connection factory object from JNDI

           ConnectionFactory cf = (ConnectionFactory) initialContext.lookup("/ConnectionFactory");
        

4. We create a JMS connection

           connection = cf.createConnection();
        

5. We start the connection

           connection.start();
        

6. We create a JMS session. The session is created as non transacted and will auto acknowledge messages.

           Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
        

7. We create a JMS message producer on the session. This will be used to send the messages.

          MessageProducer producer = session.createProducer(queue);
       

8. We create a JMS message consumer that receives 'red' messages. The message listener will check the 'color' property on each received message.

           
         MessageConsumer redConsumer = session.createConsumer(queue);
         redConsumer.setMessageListener(new SimpleMessageListener("red"));
           
         

9. We create five messages with different 'color' properties.

          
         TextMessage redMessage1 = session.createTextMessage("Red-1");
         redMessage1.setStringProperty("color", "red");
         TextMessage redMessage2 = session.createTextMessage("Red-2");
         redMessage2.setStringProperty("color", "red");
         TextMessage greenMessage = session.createTextMessage("Green");
         greenMessage.setStringProperty("color", "green");
         TextMessage blueMessage = session.createTextMessage("Blue");
         blueMessage.setStringProperty("color", "blue");
         TextMessage normalMessage = session.createTextMessage("No color");
         
        

10. We send those messages.

          
         producer.send(redMessage1);
         System.out.println("Message sent: " + redMessage1.getText());
         producer.send(greenMessage);
         System.out.println("Message sent: " + greenMessage.getText());
         producer.send(blueMessage);
         System.out.println("Message sent: " + blueMessage.getText());
         producer.send(redMessage2);
         System.out.println("Message sent: " + redMessage2.getText());
         producer.send(normalMessage);
         System.out.println("Message sent: " + normalMessage.getText());
          
        

11. Waiting for the message listener to check the received messages.

          
          Thread.sleep(5000);
         
        

12. And finally, always remember to close your JMS connections and resources after use, in a finally block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects

           finally
           {
              if (initialContext != null)
              {
                initialContext.close();
              }
              if (connection != null)
              {
                 connection.close();
              }
           }