如果文件不存在，我如何路由带有asp扩展名的URL，但如果存在，则路由到文件？

I've got a legacy site that's a hybrid of Classic ASP and WebForms/ASPX. I want to migrate the whole thing to MVC, and my first goal is to be able to route requests for ASP files to new controllers and views, as I migrate ASP to MVC. I want to make it so that a request for an ASP file that exists is handled by the file itself (legacy mode), but I want to be able to delete an ASP file and migrate its functionality to a controller and view, and have MVC detect that the file is not present, and route to the controller.I've got a legacy site that's a hybrid of Class