Beginning Java EE 6 with GlassFish 3, Second Edition

CHAPTER 13 ■ SENDING MESSAGESmethod asynchronously. Today, with EJB 3.1, asynchronous calls are possible between session beanswithout the need of MDBs, allowing them to focus on integrating systems through messaging.Reference ImplementationOpen Message Queue (OpenMQ) is the reference implementation of JMS. It has been open source since2006 and can be used in stand-alone JMS applications or embedded in an application server. OpenMQ isthe default messaging provider for GlassFish and, as this book is being written, is reaching version 4.5. Italso adds many non-standard features such as the Universal Message Service (UMS), wildcard topicdestinations, XML message validation, clustering, and more.How to Send and Receive a MessageLet’s take a look at a simple example to get an idea of JMS. JMS employs producers, consumers, anddestinations. The producer sends a message to the destination, where the consumer is waiting for themessage to arrive. Destinations can be of two kinds: queues (for point-to-point communication) andtopics (for publish-subscribe communication). In Listing 13-1, a producer sends a text message to aqueue to which the consumer is listening.Listing 13-1. The Sender Class Produces a Message into a Queuepublic class Sender {public static void main(String[] args) {// Gets the JNDI contextContext jndiContext = new InitialContext();// Looks up the administered objectsConnectionFactory connectionFactory = (ConnectionFactory)jndiContext.lookup("jms/javaee6/ConnectionFactory");Queue queue = (Queue) jndiContext.lookup("jms/javaee6/Queue");// Creates the needed artifacts to connect to the queueConnection connection = connectionFactory.createConnection();Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);MessageProducer producer = session.createProducer(queue);// Sends a text message to the queueTextMessage message = session.createTextMessage();message.setText("This is a text message sent at " + new Date());producer.send(message);}}connection.close();380