asp.net url重写有关问题

public class HttpModule : IHttpModule
    {
        private HttpContext context;
        private string Root;
        private string Url;
        public void Dispose()
        {
        }

        public void Init(HttpApplication context)
        {
            this.context = context.Context;
            Root = this.context.Request.ApplicationPath;
            context.BeginRequest += new EventHandler(Application_BeginRequest);
        }

        private void Application_BeginRequest(object sender, EventArgs e)
        {
            context = sender.To<HttpApplication>().Context;
            Url = context.Request.Url.LocalPath.ToLower();
            if (string.IsNullOrEmpty(Url.RegExReplace(Root+"/index", "")))
            {
                context.RewritePath(Root+"/Index.aspx");
            }
}
}