In a typical cfapplication tag, you'd probably use:

<cfapplication name="MyApp" applicationTimeOut="1" clientstorage="MyDSN"
 setClientCookies="Yes" sessionManagement="Yes" sessionTimeOut = ".4">

Application, Session, and Client Variable Scopes
One of the primary reasons for setting up an application with the cfapplication tag is so you can store application and session-specific data between page requests. If you do not set a cfapplication tag in a page request, you can still use variables in the application, client, or session scopes. However, there will be no way to reference the values on your next page request. You should always set up your application using the cfapplication tag.

Because variables in the application, client, and session scopes persist between requests, you often need to set them only on application or session initialization, respectively. Unfortunately, ColdFusion does not have a way to execute code when a session or application is initialized. There is a great Java workaround for this. You can read more about it in "Making the Most of J2EE Event Listeners," by Eric Brancaccio in the May 2004 edition of CFDJ. You may also want to tell Macromedia you want this feature to be in the next version of ColdFusion. If so, go to www.macromedia.com/support/email/wishform/.

Until we have that feature, there is a simple method for simulating an application or session startup. You can use a cfif to see if one of your application, session, or client variables has been defined yet. This is a simple example:

<cfif not IsDefined("application.test")>
 <cfset application.test = "Not Set Yes">
</cfif>

<cfif not IsDefined("session.test")>
 <cfset session.test = "Not Set Yet">
</cfif>

Session and application variables are called shared scope variables, because they are stored in shared memory space. You should always consider locking your shared scope variable access with the cflock tag. An in-depth explanation of locking is beyond the scope of this article. Read about the cflock tag in the live docs: http://livedocs.macromedia.com/coldfusion/6.1/htmldocs/tags-p71.htm# wp1100787. Versions of CF5 and prior had memory stability problems if you did not use locking. Read the Macromedia TechNote at www.macromedia.com/support/coldfusion/ts/documents/tn17882.htm. ColdFusion MX no longer has memory stability problems, but the best practices of locking remain relatively unchanged. You can find more information at www.macromedia.com/support/coldfusion/ts/documents/tn18235.htm.

Client variables are stored on disk, either in a database, the registry, or as cookies on the client's browser. Since they are not stored in shared memory, they do not need to be locked.

Application.cfm and OnRequestEnd.cfm
You may now be saying, "So, Jeff, that cfapplication tag seems pretty powerful. And the method for creating application and session variables is simple, yet elegant. But, I don't want to have this code on every single page. Is there a simpler way?" Well, I'm glad you asked. Yes, there is a simpler way. ColdFusion has a reserve filename, "Application.cfm", which helps us set our application variables or session variables in one place.

Application.cfm is a file that runs at the start of every request for a ColdFusion page. ColdFusion will search in the current directory, then the parent directory, and so-on, all the way up to the drive root until it finds a file called "Application.cfm". If it doesn't find one, then it continues processing normally. The Application.cfm file can be considered an implicit include, and if ColdFusion does find one, the code contained within Application.cfm will be executed (the same way that an included file is executed). That means the Application.cfm file is executed on every request for a ColdFusion page in that directory and below (provided none of the subdirectories has its own Application.cfm). This makes the Application.cfm ideal for things like the cfapplication tag, initializing application or session variables, and any other business logic you need to run at the beginning of every request.

If the ColdFusion server finds an Application.cfm file it will search in the same directory for an "OnRequestEnd.cfm" file. Just like the Application.cfm, this file (if found) will execute on every page request. Unlike Application.cfm, the OnRequestEnd.cfm executes after the page is finished processing, not before. OnRequestEnd.cfm does not typically get as much use as the Application.cfm, but it's good to know it exists, as it can be useful for footers or application cleanup at the end of each request.

Conclusion
When the Web started out, it wasn't being used for anything other than static content. As time went by people started using it for much more. ColdFusion's application framework represents a powerful mechanism for turning a simple Web site into a Web application. This article gave you the groundwork; now all that remains is for you to apply it to your development. Let me know how it goes.