public class ErrorForm  extends ActionForm{
public ActionErrors validateForm(ActionMapping mapping, HttpServletRequest request){
errs.add(FORM_KEY_ACTION_TYPE, new ActionMessage(WebGlobals.CUSTOM_ERROR));
return errs;
}
}

public class ErrorThrowingForm extends ErrorForm {
public ActionErrors postValidate(ActionMapping mapping, HttpServletRequest request)
{
    ActionErrors errs = super.validateForm(mapping, request);

    if (errs.size() > 0)
    errs.add(WebGlobals.GENERAL_ERROR_KEY, new ActionMessage(WebGlobals.PROP_FIELD_ERROR));

return errs;
}
}