private  List books =  new  LinkedList();
 public  List getBooks() {  return  books; }
 public   void  setBooks(List books) {  this .books = books; }

<logic:iterate id="book" name="testForm" property="books" indexId="index" >
  <html:text property='<%= "book[" + index + "].amount" %>'/><br>
</logic:iterate>

 public  ActionErrors validate(ActionMapping mapping, HttpServletRequest request) {
    ActionErrors errors =  super .validate(mapping, request);
    MessageResources resources = ((MessageResources) request.getAttribute(Globals.MESSAGES_KEY));
     for  (Iterator it = books.iterator(); it.hasNext();) {
      Book book = (Book) it.next();
       try  {
        Integer.parseInt(book.getCount().toString());
      }  catch  (NumberFormatException e) {
        errors.add(
          ActionMessages.GLOBAL_MESSAGE,
           new  ActionMessage("errors.integer", resources.getMessage("book.count"))
        );
      }
    }
     return  errors;
  }

 public  ActionForward execute(ActionMapping mapping,
                             ActionForm form,
                             HttpServletRequest request,
                             HttpServletResponse response)
   throws  Exception {
  HttpSession session = request.getSession();

  ActionMessages errors =  new  ActionMessages();
  
  // Проверка, если ошибка - заполняем errors, например
  errors.add(ActionMessages.GLOBAL_MESSAGE,  new  ActionMessage("book.count"));
  
  ...
  
   if  (!errors.isEmpty()) {
      saveMessages(request, errors);
    ActionForward actionForward = mapping.getInputForward();
     return  actionForward;
  }  
  
  ...

}

//saveMessages(request, errors);
saveErrors(request, errors);