Implementing an extensible factory method pattern using ASP.NET and AJAX

/*
	Copyright � 2005 Sriram Chitturi
	THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
	OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
	LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
	FITNESS FOR A PARTICULAR PURPOSE.

	You can use this code as long as this message is intact in it's form
	and give credit to the author for his work.
*/

using System;
using System.Web;
using System.IO;

namespace DataBrowser
{
	public class AjaxCallModule : IHttpModule
	{
		HttpApplication _application; // application variable used in handling the request

		public void Init(HttpApplication context)
		{
			_application = context; // save a reference to application for later use
			context.BeginRequest +=new EventHandler(context_BeginRequest);
		}
		public void Dispose()
		{
		}

		// i am using BeginRequest which is called even before Authenticate and Authorization modules
		// because the extension is unique and i can use something like x0y1z2 also for the extension !
		private void context_BeginRequest(object sender, EventArgs e)
		{
			string ext = Path.GetExtension(_application.Request.FilePath);
			if (string.Compare(ext, ".acall", true) == 0)
			{
				AjaxCallProcessor proc = new AjaxCallProcessor(_application.Request, _application.Response);
				proc.ProcessAjaxCall();

				// this following line will not be invoked as the call above is going to end the request !
				_application.CompleteRequest();
			}
		}
	}
}