4. Point-to-Point Messaging - Java Message Service, 2nd Edition [Book]
AUTO_ACKNOWLEDGE); Queue queue = mephistolessiveur.infoTemporaryQueue(); QueueSender sender = mephistolessiveur.infoSender(queue); assertNotNull(sender. Further I. QueueSender queueSender = queueSession. mephistolessiveur.info( queueSession, (Serializable) payload)); Note: mephistolessiveur.info is not on the trusted. QueueSender, QueueSession, quote server. relationship , relationships, reliable messaging, remote Index.
It is written and read sequentially. The order of entries is not defined. A message whose body contains a Java string A message whose body contains a serialized Java object.
A message whose body contains a stream of uninterpreted bytes. Producing and Consuming Messages Here are the necessary steps to develop clients to produce and consumer messages. Note that there are some common steps that shouldn't be duplicated if the client is both producing and consuming messages. Figure 1 depicts the high-level view of the steps: The following snippet of code demonstrates how to use JNDI to find a connection factory object: This can be done as follows: This is done using the Connection.
Use the Connection object to create one or more Session objects, which provide transactional context with which to group a set of sends and receives into an atomic unit of work.
A session can be created as follows: Use JNDI to find Destination object sor instantiate one directly and configure it by setting its attributes. A destination object is used by the client to specify the source of messages it consumes and the target of messages it produces.
Queue "world" ; Use a Session and a Destination object to create the needed MessageProducer object, which are used for sending messages to a destination. The code below shows how that is done.
Java Message Service, 2nd Edition by Richard Monson-Haefel, Mark Richards, David A Chappell
Note that you can create a MessageProducer object without specifying a Destination object, but in that case a Destination object must be specified for each message produced. Use a Session object and a Destination object to create any needed MessageConsumer objects that are used for receiving messages.
Once the consumer has been created, it can be used to receive messages. Message delivery, however, doesn't begin until you start the connection created earlier, which can be done by calling the start method: It is important to note that the receive method is used to consume a message synchronously.
In order to consume a message asynchronously, a message listener is used. If asynchronous communication is desired, instantiate a MessageListener object and register it with a MessageConsumer object.
QueueSession (Java EE 6 )
A MessageListener object acts as an asynchronous event handler for messages. The MessageListener interface contains one method, onMessagewhich you implement to receive and process the messages.
In the following snippet of code, the class MyListener implements the MessageListener interface. The message listener is registered with a specific consumer using the setMessageListener: One of the big benefits of JMS is that you can perform message operations as part of a transaction. When you create a QueueSession or a TopicSession, you can specify that the session is transactional.
The reason transactions are so important for messaging is that you get into situations in which you read a message off a message queue and then try to insert the message in a database. If the database operation fails, you can't just stick the message back on the queue. If the operation is transactional, however, when the database operation fails, your message stays in the queue.
Transactions can also ensure that the messaging system delivers the messages in the order you send them. Next, you use the QueueConnection to create a QueueSession. Next, you create the Queue although you usually look for the queue in the naming service first, in case someone has already created it.
When you create the queue, you must give it a name. Every queue must have a unique name. After you have a Queue, you're almost ready. All you need is a QueueSender to send messages on the queue and one or more Message objects.
- Enterprise Integration Patterns: Messaging Channels
You use the QueueSession to create both the QueueSender and the messages. In this case, the program sends "Hello" messages over a message queue. Of course, instead of creating a QueueSender, you create a QueueReceiver. There are two different ways to receive messages.
You can call the receive method, which waits for messages, or you can create a listener object that receives messages when they become available. Notice that most of the setup is the same as in Listing You tell the QueueReceiver about your message listener and it will automatically let you know when a message comes in.
Although JMS allows you to have multiple receivers on a queue, it is up to the individual implementations to decide how to handle multiple receivers. Some might distribute the messages evenly across all receivers, and others might just send all the messages to the first receiver you create. So we can't use this component as a JSF action listener. For that we need a session bean. The stateless session bean class: We have exactly one JSF action in our application, and one session bean method attached to it.
In this case, we'll use a stateless session bean, since all the state associated with our action is held by the User bean. This is the only really interesting code in the example! In this case, the attribute is injected from a context variable named user the instance variable name. Note that, since this is a sesson bean, a transaction is automatically begun when the register method is called, and committed when it completes.
A null outcome or a void action listener method redisplays the previous page.
The Java Message Service (JMS) | JMS and the Importance of Messaging | InformIT
For complex application this indirection is useful and a good practice. However, for very simple examples like this one, Seam lets you use the JSF view id as the outcome, eliminating the requirement for a navigation rule. Note that when you use a view id as an outcome, Seam always performs a browser redirect. The FacesMessages component makes it easy to display templated error or success messages. Built-in Seam components may be obtained by injection, or by calling an instance method. Note that we did not explicitly specify a Scope this time.
Each Seam component type has a default scope if not explicitly specified. For stateless session beans, the default scope is the stateless context. Actually, all stateless session beans belong in the stateless context. Our session bean action listener performs the business and persistence logic for our mini-application. In more complex applications, we might need to layer the code and refactor persistence logic into a dedicated data access component.
That's perfectly trivial to do. But notice that Seam does not force you into any particular strategy for application layering. Furthermore, notice that our session bean has simultaneous access to context associated with the web request the form values in the User object, for exampleand state held in transactional resources the EntityManager object. This is a break from traditional J2EE architectures.
Again, if you are more comfortable with the traditional J2EE layering, you can certainly implement that in a Seam application. But for many applications, it's simply not very useful. The session bean local interface: Now onto the deployment descriptors. The Seam component deployment descriptor: You'll be relieved to know that Seam does not require that application components be accompanied by XML.
Most Seam applications require a very small amount of XML that does not grow very much as the project gets bigger. Nevertheless, it is often useful to be able to provide for some external configuration of some components particularly the components built in to Seam. You have a couple of options here, but the most flexible option is to provide this configuration in a file called components. We'll use the components.
The funny symbols are there because our Ant build script puts the correct JNDI pattern in when we deploy the application. The web deployment description: So we'll need a web deployment descriptor. The configuration you see here is pretty much identical in all Seam applications. So usually we'll need faces-config. In our case, we are going to use Facelets for defining our views, so we need to tell JSF to use Facelets as its templating engine.
Our managed beans are annotated Seam components. In Seam applications, the faces-config. In fact, once you have all the basic descriptors set up, the only XML you need to write as you add new functionality to a Seam application is orchestration: Seam takes the view that process flow and configuration data are the only things that truly belong in XML.
In this simple example, we don't even need a navigation rule, since we decided to embed the view id in our action code.
The EJB deployment descriptor: The EJB persistence deployment descriptor: In this case, enables automatic schema export at startup time. In this example we use Facelets, because we think it's better than JSP.
There is nothing specific to Seam here. The EAR deployment descriptor: We've now seen all the files in the entire application! Since there is no value already bound to that name in any Seam contextSeam instantiates the user component, and returns the resulting User entity bean instance to JSF after storing it in the Seam session context. The form input values are now validated against the Hibernate Validator constraints specified on the User entity.
If the constraints are violated, JSF redisplays the page. Otherwise, JSF binds the form input values to properties of the User entity bean.