I am creating my own channel for Roku. I need to get the streams of my videos and images from a JSON file from a server. I found a couple of examples of how to do that using roUrlTransfer component, but all those examples tell that you need to have a web service first to get the JSON or xml file from it, and I'm not really familiar with creating web services. Can I just put a JSON file on my server and get that using roUrlTransfer instead of having a web service to generate that file for me?
Yes, as long as the url is accessible to the Roku, you can host it as a static json or xml file. You don't need a full blown web service.
In fact, a significant number of the channels available on the Roku are driven by static MRSS feeds.