How to use Session and Application variables in an ASP program

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SUMMARY

This step-by-step procedure demonstrates how to set and retrieve information from both Session and Application objects in an Active Server Pages (ASP) application.

Session and Application variables basics

You can use the Application and Session objects to store values that are global rather than page-specific for either a particular user (the Session) or to all users (the Application).

The Session and Application variables are stored on the server. Client browsers are then attached to the session through a cookie. As a result, the client must have cookies enabled in the browser for Session and Application variables to work.

The samples to follow demonstrate how to use Visual InterDev to create Session and Application variables.

Create a Visual InterDev Web project

  1. Create a new Web Project in Visual InterDev. For detailed instructions, see the following article in the Microsoft Knowledge Base:
    301184 How to create a Visual InterDev project
  2. From the Project menu, point to Add Web Item, and then click Active Server Page.
  3. Click Open to accept the default information for the new ASP page.
Now that you added an ASP page to the current project, the ASP code samples in the next two sections demonstrate the use of both Session and Application variables.

How to use Session variables

The power of the Session object comes from the fact that it can store variables that are global to just that specific user; as a result, each user can have their own individual value for that variable. Session objects are not always created automatically for every user when they enter your application. However, storing or accessing a variable in the Session object creates the Session object and fires the Session_OnStart event.

To demonstrate how to use the Session object in an ASP page, follow these steps:
  1. Paste the following code between the <BODY> </BODY> tags of the ASP page that you created earlier in Visual InterDev:
    <%
       'Store information in a Session variable.
       Session("myInformation") = "somevalue"
    
       'Display the contents of the Session variable.
       Response.Write Session("myInformation")
    %>
    					
  2. Click View in Browser from the View menu.
  3. When you are prompted to save the file, click OK. The browser displays the information in the variable.

How to use Application variables

Think of the Application object as a global container for information that is available to all pages of your ASP application. You can store variables and object references in the Application object. The Application object is instantiated when the first page of your application is requested and remains available until the Web service is shut down.

To demonstrate how to use the Application object in an ASP page, follow these steps:
  1. Paste the following code between the <BODY> </BODY> tags of the ASP page that you created earlier in Visual InterDev:
    <%
       'Store information in an Application variable.
       Application("myvalue") = "something"
    
       'Display the contents of the Application variable.
       Response.Write Application("myvalue")
    %>
    					
  2. Click View in Browser from the View menu.
  3. When you are prompted to save the file, click OK. The browser displays the information in the variable.

Application_OnStart and Session_OnStart events

You can use both the Application_OnStart and Session_OnStart events to initialize state. To do this, set up variables that are global for either the application or a specific user. When the first user accesses a file in your application, the Application_OnStart event is triggered. This event is used to initialize any application-wide global variables. When the user begins a session for the first time, the Session_OnStart event is triggered. This event is used to initialize user-specific information.

Application_OnEnd and Session_OnEnd events

The Session_OnEnd event occurs either when a current session times out. By default, this is 20 minutes after the last request for a page from the application. To change this default time out setting, you can set the Session.Timeout property or edit the registry.

You can use the Application_OnEnd event to clean up all of the global objects and variables. However, in a present problem, this event may not be triggered until the Web server is stopped. Revisions of ASP seem likely to specify that the Application_OnEnd event be triggered once the last Session_OnEnd event occurs, that is, when the last session ends and there are no current application users.

Troubleshooting

Application and Session variables require that clients have cookies enabled in their Web browser, which is not reliable between shared frames in a frameset or across multiple browser instances.

Session and Application events are only triggered when a client retrieves an ASP page; they are not triggered when an HTML page in the application is requested. Therefore, if you have additional server-side applications such as Internet Server Application Programming Interface (ISAPI) or Common Gateway Interface (CGI) scripts, make sure that these applications do not depend on specific events having occurred within an ASP page. Otherwise, the ISAPI or CGI script may fail (crash) and cause the Web server to stop responding (hang).

This method stores information on the Web server. This decreases scalability in two ways: Session and Application variables use resources on the server and cannot be used on completely load balanced Web Farms.

REFERENCES

For more information, see the following Microsoft Web sites:
Avoiding traps when using the Application and Session objects
Using variables and constants
http://www.microsoft.com/windows/windows2000/en/datacenter/iis/htm/asp/iiwavar.htm

Active Server Pages guide
http://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/iisbook/c06_active_server_pages.mspx?mfr=true

ASP scripting optimization
http://www.microsoft.com/windows/windows2000/en/advanced/iis/htm/asp/perf9ini.htm
For more information, click the following article numbers to view the articles in the Microsoft Knowledge Base:
281298 PRB: Session variables do not persist when application contains empty Global.asa
230149 How to access Session and Application variables from within a Visual Basic component

Properties

Article ID: 300883 - Last Review: March 29, 2007 - Revision: 3.2
APPLIES TO
  • Microsoft Active Server Pages 4.0
  • Microsoft Visual InterDev 1.0 Standard Edition
  • Microsoft Visual InterDev 6.0 Standard Edition
Keywords: 
kbaspobj kbhowto kbhowtomaster kbsample kbscript KB300883

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