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ASP.NET in a Nutshell by Matthew MacDonald, G. Andrew Duthie

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Chapter 13. The HttpApplicationState Class

Developers who are new to Web-based development encounter several challenges. Among the most serious is the realization that rather than a single monolithic application, web-based applications are just a series of pages. A web server is like an unusually inattentive waiter. Imagine sitting down for dinner and placing your order for drinks. When you next see the waiter, he asks you again what you would like to drink, as if he has never seen you before. Each request to the web browser is seen as a completely new request, totally unrelated to any previous request.

Several problems with the way Web-based applications are structured need to be resolved:

  • Session data (data specific to a single user across all pages) needs to be available. While it is always a good idea to minimize session state, it is generally not possible to completely eliminate session state.

  • Global data (data required across all pages and to all users) needs to be exposed. Traditional rich-client applications use global variables to store needed data application-wide. Classes instantiated on one page are not available to other pages, so creating global classes is not a solution.

Session data in ASP.NET can be managed in the HttpSessionState class, which will be covered in Chapter 19. Global data can be stored in the HttpApplicationState class, which is covered in this chapter.

ASP.NET creates the illusion that pages are grouped into an application. An instance of the

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