HttpApplication

HttpApplication is a class in the System.Web namespace of the .NET Framework that represents the ASP.NET application object. It provides the application-wide context and serves as the host for the HttpModule pipeline, coordinating how requests are processed within an ASP.NET application.

In typical use, developers create a Global.asax file that derives from HttpApplication or handles its events. The class defines a set of application and request lifecycle events, such as Application_Start and Application_End (which run once per application domain lifecycle), Session_Start and Session_End (per user session), and a range of request events including BeginRequest, AuthenticateRequest, AuthorizeRequest, ResolveRequestCache, AcquireRequestState, PreRequestHandlerExecute, PostRequestHandlerExecute, ReleaseRequestState, UpdateRequestCache, and EndRequest. These events allow code to run at precise points in the processing of a request or the overall application lifecycle.

HttpApplication exposes access to the current HttpContext and to application-wide state via HttpApplicationState, enabling shared data across requests and sessions. Modules in the ASP.NET pipeline subscribe to these events to implement cross-cutting concerns such as authentication, caching, logging, and custom processing.

In summary, HttpApplication is a central component of the ASP.NET request-processing model in the .NET Framework, embodying the application’s lifecycle and providing hooks for per-application and per-request code. It is part of the classic ASP.NET pipeline and, with the advent of ASP.NET Core, has been superseded by a middleware-based approach using IApplicationBuilder.