Asynchronous JavaScript Technology and XML (AJAX) With Java 2

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Asynchronous JavaScript Technology and XML (AJAX) With Java 2: "Some uses for AJAX interactions are the following:

• Real-Time Form Data Validation: Form data such as user IDs, serial numbers, postal codes, or even special coupon codes that require server-side validation can be validated in a form before the user submits a form.


• Autocompletion: A specific portion of form data such as an email address, name, or city name may be autocompleted as the user types.


• Master Details Operations: Based on a client event, an HTML page can fetch more detailed information on data such as a product listing that enables the client to view the individual product information without refreshing the page.


• Sophisticated User Interface Controls: Controls such as tree controls, menus, and progress bars may be provided that do not require page refreshes.


• Refreshing Data on the Page: HTML pages may poll data from a server for up-to-date data such as scores, stock quotes, weather, or application-specific data.


• Server-side Notifications: An HTML page may simulate a server-side push by polling the server for event notifications that may notify the client with a message, refresh page data, or redirect the client to another page.

This list is not all-inclusive, but it shows that AJAX interactions allow web applications to do much more than they have done in the past. Although many of these benefits are noteworthy, this approach has some drawbacks as well:

• Complexity: Server-side developers will need to understand that presentation logic will be required in the HTML client pages as well as in the server-side logic to generate the XML content needed by the client HTML pages. HTML page developers must have JavaScript technology skills. Creating AJAX-enabled applications will become easier as new frameworks are created and existing frameworks evolve to support the interaction model.


• Standardization of the XMLHttpRequest Object: The XMLHttpRequest object is not yet part of the JavaScript technology specification, which means that the behavior may vary depending on the client.


• JavaScript Technology Implementations: AJAX interactions depend heavily on JavaScript technology, which has subtle differences depending on the client. See QuirksMode.org for more details on browser-specific differences.


• Debugging: AJAX applications are also difficult to debug because the processing logic is embedded both in the client and on the server.


• Viewable Source: The client-side JavaScript technology may be viewed simply by selecting View Source from an AJAX-enabled HTML page. A poorly designed AJAX-based application could open itself up to hackers or plagiarism."