CIS 451: ASP Sessions and Applications

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CIS 451 ASP Sessions and Applications

• Dr. Ralph D. Westfall
• January, 2009

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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

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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

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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

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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

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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

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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)

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Session Object Methods

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

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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

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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)

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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

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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

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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

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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

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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