They will probably move this over to the struts
thread.
Anyhow, depending on how big your application is, you would probably want to just do everything by hand. How familiar are you with struts? I would think that once you are familiar with how to build struts apps, you could take an existing app and systematically break it down. That is what I have had to do at my place of employment. If you plan on using the validation framework(which I highly recommend), you will need to do a lot of changes as well.
Struts is awesome, but I don't think there is any clean way to just convert it all over. The process will really solidify your knowledge though.