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    <ul> <li>If your frequency is not that high (1min), polling from a browser in a database is OK, especially if you already have a database in your application, a job scheduler like Quartz, and you are using "only" a servlet container.</li> <li>If response times are important, consider using asynchronous servlets. Again on the server side, one thread can poll a database, and handle multiple clients efficiently.</li> </ul> <p>As for JMS</p> <ul> <li>As an alternative replace the database and the scheduler with JMS queues and message driven beans (MDB). The main difference is the programming model: Instead of <strong>polling</strong>, your receivers <strong>listen</strong>: They <em>get</em> notified. This way the framework can choose the best method to implement message delivery. In addition to a standard servlet container you now need a JMS provider, and possibly an EJB container.</li> <li>You can combine this with asynchronous servlets as well.</li> </ul> <p>If you do not use a database in the first approach: JMS supports persistent messages out-of-the-box, and the queues decouple client and worker by buffering the messages. This simplifies system maintenance: You can update the application with the workers without interrupting the clients.</p> <p><em>Update</em></p> <p>Message sender and receiver are decoupled by the message (it's asynchronous). So processing in the receiver is not stopped by any action in the user interface.</p> <p>For example</p> <ol> <li>The servlet sends a message. It returns immediately a HTML response to the user/browser: "Task has been submitted". It's asynchronous, because it does not wait for the result.</li> <li>The receiver gets the message, and starts processing, for example an MDB in its <code>onMessage</code> method</li> <li>The HTML page is refreshed: The servlet now checks, if there is a message in the response queue. There is none so far, so it returns "not yet completed".</li> <li>The receiver has finished its calculations, and puts the result as a message on the result queue.</li> <li>The HTML page is refreshed: Now there is a message, and it will present the results to the user.</li> </ol> <p>If you implement the checking as an AJAX call, the user does not see that you are actually polling.</p>
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    1. COsince i am new to JMS , please tell me if the listener gets notified and then starts doing the processing , will the processing stop if i click on some other link from my web application and the controls goes to the other controller...or listener will work in a separate thread....and continue processing , Assuming the listener class is in the same WAR.
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      1. USManish Sahni
    2. CO@ManishSahni I have added an example to the answer. Think of messaging like a postal service: You have a letter, put it in a letter box, and the next days you are waiting for the postman. Three days later, he gives you the response (another letter). So once you have put the letter in the letter box, you cannot interrupt it, you have to wait. Of course the receiver is free to discard your letter, and is free not to respond at all.
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    3. COWow, that's a crisp and great explanation..It really helped in understanding the concept.
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Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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