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public class ValidateOutput {
  // Allows only alphanumeric characters and spaces
  private static final Pattern pattern = Pattern.compile("^[a-zA-Z0-9\\s]{0,20}$");

  // Validates and encodes the input field based on a whitelist
  public String validate(String name, String input) throws ValidationException {
    String canonical = normalize(input);

    if (!pattern.matcher(canonical).matches()) {
      throw new ValidationException("Improper format in " + name + " field");
    }
    
    // Performs output encoding for nonvalid characters 
    canonical = HTMLEntityEncode(canonical);
    return canonical;
  }

  // Normalizes to known instances 	
  private String normalize(String input) {
    String canonical = 
      java.text.Normalizer.normalize(input, Normalizer.Form.NFKC);
    return canonical;
  }

  // Encodes nonvalid data
  private static String HTMLEntityEncode(String input) {
    StringBuffer sb = new StringBuffer();

    for (int i = 0; i < input.length(); i++) {
      char ch = input.charAt(i);
      if (Character.isLetterOrDigit(ch) || Character.isWhitespace(ch)) {
        sb.append(ch);
      } else {
        sb.append("&#" + (int)ch + ";");
      }
    }
    return sb.toString();
  }
}
 
// ...
 
@RequestMapping("/getnotifications.htm")
public ModelAndView getNotifications(HttpServletRequest request, HttpServletResponse response) {
  ValidateOutput vo = new ValidateOutput();

  ModelAndView mv = new ModelAndView();
  try {
    UserInfo userDetails = getUserInfo();
    List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();
    List<Notification> notificationList = 
        NotificationService.getNotificationsForUserId(userDetails.getPersonId());
           
    for (Notification notification: notificationList) {
      Map<String,Object> map = new HashMap<String,Object>();
      map.put("id", vo.validate("id", notification.getId()));
      map.put("message", vo.validate("message", notification.getMessage()));
      list.add(map);
    }
            
     mv.addObject("Notifications", list);
  }
  catch(Throwable t) {
    // Log to file and handle
  }
 
  return mv;
}