Sample web app: upload file, process it, download

I'm trying to make my first web app using Grails.

I want to upload a file, process it and return for download. I think it's a very common scheme and I believe there should be some sample app that does that.

I would like to use such and only change the processing part, implementing my own. It'd be the best if it was in Grails, but I guess anything else will work too. Well, the only problem might be that I have written my processing part in Groovy.

The help I'm seeking from you is whether you could provide me a source of such sample app/sample code/template so I could right away start implementing the processing part.

Obviously I've been searching for one to no avail.

I'm a newbie when it comes to web apps; I've only programmed some simple desktop apps, so if my question is inappropriate I'm terribly sorry.

Thanks in advance for all answers.