Validation HashMap->Radiobutton. Struts2

I have another problem! :)

I have a hashmap linked on jsp with a radiobutton. When I check a radio, my hashmap is populated with the param that I spec on the tag. Now I want to validate the check on radiobutton. How can I make this? Is possible with the annotations?

I have just found a solution, using an another list. But I'm sure that exist another way, too simple and clean. With the annotatio开发者_如何学编程ns.. Exist?

Here's the Struts Validation document. You likely need the Required Validator which is also available in flavor of an annotation: @RequiredFieldValidator.