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CIS 451: ASP Sessions and Applications

CIS 451: ASP Sessions and Applications. Dr. Ralph D. Westfall January, 2009. State Handling. http server only processes requests for web pages, images, etc. this is a "stateless" connection server sends page, etc. and writes some tracking data to a log file

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CIS 451: ASP Sessions and Applications

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  1. CIS 451: ASP Sessions and Applications Dr. Ralph D. Westfall January, 2009

  2. State Handling • http server only processes requests for web pages, images, etc. • this is a "stateless" connection • server sends page, etc. and writes some tracking data to a log file • but does NOT store any information in its memory about the request

  3. State Handling - 2 • ASP.NET can store some information in memory in relation to web site visitors, which can be used to: • make frequently used/updated information available to several/all pages in site • store information about a page so it will be available when page is loaded again • pass information between pages

  4. Definitions • Application: group of web pages working together for a common purpose • often in same directory or its subdirectories • Session: a client accessing an application • Cookie: data stored by the application on a client's computer

  5. Session State • session starts when a user accesses a page • ends after a time period, or when closed by ASP code • data can be stored in "session variables" • stored in Session Contents collection • available until session ends, then lost • user's browser must accept cookies • without cookies, can't use session variables

  6. Accessing Contents Collection • session contents "indexed" by "keys" • writing to Session contents: • Session("intCount") = intCount • reading from Session contents: • intNumber = Session("intCount") • variable name before = does NOT have to match names of keys when reading or writing • using same names can help in maintenance

  7. Session Object Properties • SessionID: unique identifier for session • Timeout : when session ends if no activity (default often is 20 minutes) • Session.Timeout = 30 'ends 30 minutes • international settings (currency) • CodePage (sets character alphabet) • LCID (locale ID values set time zone and other location information, but only if installed on server)

  8. Session Object Methods • Abandon: ends session before it times out • Session.Abandon() • removing Session contents data Session.Clear()

  9. Problem with Session Variables • user's browser must accept cookies • without cookies, can't use session variables • alternative: userID and password • requires customer to establish an account • data stored in database on server • requires writing extra HTML code into each page (hidden form fields) to identify the user who is requesting another page

  10. Application State • includes variables that can be available to all pages in the "application" • variables can be set/changed from a web page via authorized inputs • can also be stored in a Global.asax file • value loads into memory every time server is turned on (but changing a value(s) in memory does NOT update this file)

  11. An Application • includes all files in a virtual directory ("root"), and in its subdirectories • starts when first client opens any of files • can have many sessions (users) accessing it at the same time (simultaneously) • number of sessions limited only by available memory of server

  12. An Application - 2 • continues until server shuts down • usually means something went wrong • also ends when application is "unloaded" from server • can use Microsoft Management Console to unload

  13. Application State Items • are stored data useable in all sessions • stored in Application Contents collection • "initialized" in Global.asax file (can view in Visual Studio) in application's root directory • Sub Application_Start(ByVal sender _ As Object, ByVal e As EventArgs) • Application("dblPrice1") = 1.50 • Application("dblPrice2") = 2.75 • End Sub

  14. Accessing Application State Items • reading is like reading Session variables • dblPrice(1)= Application("dblPrice1") • writing requires "concurrency control" • Application.Lock() • Application("hits") += 1 • Application.Unlock() • lock so other users can't access until done • writing overrides values in Global.asax file • does NOT change contents of Global.asax

  15. Global.asax and Web.config • Global.asax: settings that won't change • use Web.config file for anything that could change instead of Global.asax • can store objects as well as variables e.g., connection string • if either file has a lot of items, check code to avoid duplications in other files

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