Queuesession and queuesender relationship

Sender JMS Client Example

queuesession and queuesender relationship

Figure shows the relationship between connections, sessions, You use the QueueSession to create both the QueueSender and the. A JMS client assumes that the JMS resources (such as a queue connection . QueueSession, QueueSender, and QueueReceiver) when the resources are no . The queue sender is a small convenience program that simply sends a text the connection | promovare-site.info(); | | // create a queue session | QueueSession.

This parameter defines how long the method should wait if there is no message available immediately.

queuesession and queuesender relationship

If you omit this parameter, the call blocks indefinitely. If you do not want any delay, use the receiveNoWait method. In this example, the receive call returns when the message arrives, or after ms, whichever is sooner. Act on the message received. When a message is received, you can act on it as needed by the business logic of the client.

queuesession and queuesender relationship

Some general JMS actions are to check that the message is of the correct type and extract the content of the message. To extract the content from the body of the message, cast from the generic Message class which is the declared return type of the receive methods to the more specific subclass, such as TextMessage.

It is good practice always to test the message class before casting, so that unexpected errors can be handled gracefully. In this example, the instanceof operator is used to check that the message received is of the TextMessage type.

The message content is then extracted by casting to the TextMessage subclass.

  • Developing a JMS client
  • Point to Point Messaging Program

If the application needs to create many short-lived JMS objects at the Session level or lower, it is important to close all the JMS resources used. To do this, you call the close method on the various classes QueueConnection, QueueSession, QueueSender, and QueueReceiver when the resources are no longer required.

The exceptions are that topic resources are used instead of queue resources such as TopicPublisher instead of QueueSenderas shown in the following example to publish a message: It is good programming practice to catch these exceptions and display them on a suitable output.

The first parameter in the createQueueSession method decides whether or not the session is transacted. Here, we use a non-transacted session. The second parameter decided the delivery mode, which is never used for sending applications. Create a queue sender for queue0 and create a message. Send the "Hello" message to queue0.

queuesession and queuesender relationship

Close the queue connection. This will in turn close both the session and the QueueSender.

Router Sample Program

The full source code for the sender application is shown below: This means that the message will be lost in case the JMS server crashes. Instead of a QueueSender object, the receiver application creates a QueueReceiver from which messages can be received synchronously.

Note that the receiver application must start the connection before any messages can be received. The receiver application uses a non-transacted session with automatic message acknowledgement.

This means that message will automatically be acknowledged by the session right before the receive method returns the message to the application. Below is the source for the Receiver class: 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.

queuesession and queuesender relationship

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. Note Because sessions are single-threaded, you can only process one message at a time. If you need to process multiple messages concurrently, you must create multiple sessions.

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Publishing Messages Although the overall concept of publish-subscribe is a bit different from point-to-point messages, the JMS calls for creating a topic and publishing messages are remarkably similar to the calls for sending queue messages.

In fact, if you go through the program in Listing You must also change the createSender call to createPublisher. As with queues, each topic must have a unique name.

Unlike queues, in which you only have one receiver, you normally have many subscribers to a topic. You can also have multiple publishers.

Developing a JMS client

Your clients will just see more messages than they do if only one copy is running. Subscribing to Topics Subscribing to a topic is just as easy as listening on a queue. Again, you can just about convert the program in Listing The actual listener implementation for topics is identical to the one for queues.

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Durable Subscriptions Most pub-sub systems you see today deal with frequently published data and tend to provide real-time monitoring and status updates. Pub-sub is good for these kinds of operations.