Programming ASP.NET, Second Edition

Controlling the Application

Now that an application has been defined, you will see how applications can be controlled globally. There are two ways of doing this: using the HttpApplication object and using the global.asax file.

HttpApplication Object

Just as a web page instantiates the Page class, when an application runs, it instantiates an object from the HttpApplication class. This object has methods, properties, and events that are available to all the objects within the application. It provides several objects that allow you to interact with the HTTP request. These include:

• The Application object for using application state

• The Request object for getting access to the incoming request

• The Response object for sending an HttpResponse back to the client

• The Session object for access to session state

ASP.NET maintains a pool of HttpApplication instances during the lifetime of each application. Every time a page is requested from the server, an HttpApplication instance is assigned to it. This instance manages the request from start to end. Once the request is completed, that instance is freed up for reuse.

You can program against the HttpApplication object by using a file called global.asax, described in the next section.

global.asax

Any code contained in the global.asax file becomes part of the application in which it is located There can be only a single global.asax file per application, located in the virtual root directory of the application. However, this file is optional. If there ...