Validating and parsing url parameters in ASP.NET

[deqmbvr]

I'm maintaining a legacy WebForms application and one of the pages just serves GET requests and works with many query string parameters. This work is done in the code-behind and does a lot of this type of check and casting.\[code\]protected override void OnLoad(EventArgs e){ string error = string.Empty; string stringParam = Request.Params["stringParam"]; if (!String.IsNullOrEmpty(stringParam)) { error = "No parameter"; goto LoadError; } Guid? someId = null; try { someId = new Guid(Request.Params["guidParam"]); } catch (Exception){} if (!someId.HasValue) { error = "No valid id"; goto LoadError; } // parameter checks continue onLoadError: log.ErrorFormat("Error loading page: {0}", error); // display error page}\[/code\]I'd like to create a testable class that encapsulates this parsing and validation and moves it out of the code-behind. Can anyone recommend some approaches to this and/or examples?