Introduction
Global.asax is an optional file used to declare and handle application and session level events and objects. Global.asax is the ASP.NET extension of the ASP Global.asa file. The Global.asax file resides in the IIS virtual root of an ASP.NET application. At run time, upon the arrival of the first request, Global.asax is parsed and compiled into a dynamically generated .NET Framework class. ASP.NET is configured so that any direct request for the Global.asax is automatically rejected, external users cannot view or download the code in it.
Main
Code to handle application events, such as the start and end of an application, resides in Global.asax. Such event code cannot reside in the ASP.NET page or web service code itself, since during the start or end of the application, its code has not yet been loaded. Global.asax is also used to declare data that is available across different application requests or across different browser sessions. This process is known as application and session state management.
You can create a Global.asax file either in a WYSIWYG designer or as a compiled class that you deploy in your application's \Bin directory as an assembly. However, in the latter case, you still need a Global.asax file that refers to the assembly.
How to create Global.asax
Adding a Global.asax to your web project is quiet simple.
Open Visual Studio 2005 or 2008 > Create a new website > Go to the Solution Explorer > Add New Item > Global Application Class > Add.
Examining the methods related to the events in Global.asax
There are 2 ‘set’ of methods that fire corresponding to the events. The first set which get invoked on each request and the second set which does not get invoked on each request. Let us explore these methods.
Methods corresponding to events that fire on each request
Application_BeginRequest() – fired when a request for the web application comes in.
Application_AuthenticateRequest –fired just before the user credentials are authenticated. You can specify your own authentication logic over here.
Application_AuthorizeRequest() – fired on successful authentication of user’s credentials. You can use this method to give authorization rights to user.
Application_ResolveRequestCache() – fired on successful completion of an authorization request.
Application_AcquireRequestState() – fired just before the session state is retrieved for the current request.
Application_PreRequestHandlerExecute() - fired before the page framework begins before executing an event handler to handle the request.
Application_PostRequestHandlerExecute() – fired after HTTP handler has executed the request.
Application_ReleaseRequestState() – fired before current state data kept in the session collection is serialized.
Application_UpdateRequestCache() – fired before information is added to output cache of the page.
Application_EndRequest() – fired at the end of each request
Methods corresponding to events that do not fire on each request
Application_Start() – fired when the first resource is requested from the web server and the web application starts.
Session_Start() – fired when session starts on each new user requesting a page.
Application_Error() – fired when an error occurs.
Session_End() – fired when the session of a user ends.
Application_End() – fired when the web application ends.
Application_Disposed() - fired when the web application is destroyed.
I will try to compile and add some example about global.asax in a short time.
Conclusion
In this article, we learnt that Global.asax is a file used to declare application-level events and objects. The file is responsible for handling higher-level application events such as Application_Start, Application_End, Session_Start, Session_End, and so on. I would encourage you to explore the methods corresponding to the events and analyze the best possible methods to use them in your application, if needed.