HttpApplication is the default base class from which your web application derives. This class is most notable for the application-level events it provides. You can code event handlers that react to global application events in the global.asax file. If you use Visual Studio .NET to create a code-behind class (like global.asax.vb), the event handler code will be created in a class called Global, which inherits from HttpApplication.

The first time a user navigates to a page in your application, the ASP.NET engine creates a pool of HttpApplication objects. Whenever your application receives a request, the ASP.NET engine automatically assigns one of these HttpApplication instances to serve the request. This HttpApplication instance will be reused, but only once the request is complete.

public class HttpApplication : IHttpAsyncHandler, IHttpHandler, System.ComponentModel.IComponent, IDisposable {
// Public Constructors
   public HttpApplication( );
// Public Instance Properties
   public HttpApplicationState Application{get; }
   public HttpContext Context{get; }
   public HttpModuleCollection Modules{get; }
   public HttpRequest Request{get; }
   public HttpResponse Response{get; }
   public HttpServerUtility Server{get; }
   public HttpSessionState Session{get; }
   public ISite Site{set; get; }                    // implements System.ComponentModel.IComponent
   public IPrincipal User{get; }
// Protected Instance Properties
   protected EventHandlerList Events{get; }
// Public Instance Methods
   public void AddOnAcquireRequestStateAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnAuthenticateRequestAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnAuthorizeRequestAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnBeginRequestAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnEndRequestAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnPostRequestHandlerExecuteAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnPreRequestHandlerExecuteAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnReleaseRequestStateAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnResolveRequestCacheAsync(BeginEventHandler bh, EndEventHandler eh);
   public void AddOnUpdateRequestCacheAsync(BeginEventHandler bh, EndEventHandler eh);
   public void CompleteRequest( );
   public virtual void Dispose( );                   // implements IDisposable
   public virtual string GetVaryByCustomString(HttpContext context, string custom);
   public virtual void Init( );
// Events
   public event EventHandler AcquireRequestState;
   public event EventHandler AuthenticateRequest;
   public event EventHandler AuthorizeRequest;
   public event EventHandler BeginRequest;
   public event EventHandler Disposed;              // implements System.ComponentModel.IComponent
   public event EventHandler EndRequest;
   public event EventHandler Error;
   public event EventHandler PostRequestHandlerExecute;
   public event EventHandler PreRequestHandlerExecute;
   public event EventHandler PreSendRequestContent;
   public event EventHandler PreSendRequestHeaders;
   public event EventHandler ReleaseRequestState;
   public event EventHandler ResolveRequestCache;
   public event EventHandler UpdateRequestCache;
}

Returned By

HttpContext.ApplicationInstance

Passed To

HttpContext.ApplicationInstance, IHttpModule.Init( ), System.Web.Security.DefaultAuthenticationModule.Init( ), System.Web.Security.FileAuthorizationModule.Init( ), System.Web.Security.FormsAuthenticationModule.Init( ), System.Web.Security.PassportAuthenticationModule.Init( ), System.Web.Security.UrlAuthorizationModule.Init( ), System.Web.Security.WindowsAuthenticationModule.Init( ), System.Web.SessionState.SessionStateModule.Init( )