void Application_BeginRequest(object sender, EventArgs e)
    {

        string fullOrigionalpath = Request.Url.ToString();

        if (fullOrigionalpath.Contains("/Docs/"))
        {
            int i = fullOrigionalpath.LastIndexOf("/Docs/");
            string file = fullOrigionalpath.Substring(i+6);
            
            string conn = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
            SqlConnection sqlConnection1 = new SqlConnection();
            sqlConnection1.ConnectionString = conn;

            SqlCommand CmdInsertFile = new SqlCommand("select id from docs where filename=@filename", sqlConnection1);
            CmdInsertFile.Parameters.AddWithValue("@filename", file);
            sqlConnection1.Open();
            string id = CmdInsertFile.ExecuteScalar().ToString();
            sqlConnection1.Close();
            Context.RewritePath("~/FileStream.ashx?FileId="+id);
        }
    }