Select radio button after false validation


I have a form containing two radio buttons generated through a radioButtonList(). None of the radio buttons is selected once the view gets rendered.

However, it is required to select one radio button.

Now if the user did not select a radio button and the validation returns an error I would like to have one radio button selected within the returned form.

How would you approach this problem?

Could this be done with afterValidation()?

Thanks a lot,