Beginning Java EE 6 with GlassFish 3, Second Edition

CHAPTER 13 ■ SENDING MESSAGESJava Messaging ServiceAt a high level, the JMS architecture consists of the following components (see Figure 13-2):• A provider: JMS is only a specification, so it needs an underlying implementationto route messages, that is, the provider (aka a message broker). The providerhandles the buffering and delivery of messages by providing an implementation ofthe JMS API.• Clients: A client is any Java application or component that uses the JMS API toeither consume or produce a JMS message. Such a client is known as a JMS clientbecause it is a client of the underlying provider. “Client” is the generic term forproducer, sender, publisher, consumer, receiver, or subscriber.• Messages: These are the objects that clients send to or receive from the JMSprovider.• Administered objects: A message broker must provide administered objects to theclient (connection factories and destinations) either through JNDI lookups orinjection (as you’ll see later).Figure 13-2. JMS architectureThe messaging provider enables asynchronous communication by providing a destination wheremessages can be held until they can be delivered to a client. There are two different types of destination,each applying to a specific messaging model:• The point-to-point (P2P) model: In this model, the destination used to holdmessages is called a queue. When using point-to-point messaging, one client putsa message on a queue, and another client receives the message. Once the messageis acknowledged, the message provider removes the message from the queue.382