When a visitor first requests an .aspx page on your server, the server sends it to the HTTP Pipeline. The HTTP Pipeline handles all processes involved in converting all of the application code into HTML to be interpreted by the browser. The first class initiated is called HttpRuntime. This class finds a free HttpApplication object to start processing the request. The HttpApplication object then runs the appropriate handler assigned in the web.config and machine.config files for the requested extension.
The extension .aspx can be handled by the HandlerClass or HandlerFactory class. The HttpApplication objects starts the IHttpHandler interface which begins processing the application code by calling the processRequest() method.
The processRequest() method then calls the FrameworkInitialize() method which begins building the control trees for the requested page. Now the processRequest() method cycles through the page’s life cycle in the order listed below.