code: public void validateParameters() {
  
          // localisation
          CmsMessages messages = Messages.get().getBundle(getLocale());
  
          StringBuffer validationErrors = new StringBuffer();
          if (CmsStringUtil.isEmpty(getParamResource())) {
              validationErrors.append(messages.key(Messages.GUI_ELEM_RENAME_VALIDATE_RESOURCE_FOLDER_0)).append("<br>");
          }
          if (CmsStringUtil.isEmpty(getParamTemplate())) {
              validationErrors.append(messages.key(Messages.GUI_ELEM_RENAME_VALIDATE_SELECT_TEMPLATE_0)).append("<br>");
          }
          if (CmsStringUtil.isEmpty(getParamLocale())) {
              validationErrors.append(messages.key(Messages.GUI_ELEM_RENAME_VALIDATE_SELECT_LANGUAGE_0)).append("<br>");
          }
          if (CmsStringUtil.isEmpty(getParamOldElement())) {
              validationErrors.append(messages.key(Messages.GUI_ELEM_RENAME_VALIDATE_ENTER_OLD_ELEM_0)).append("<br>");
          }
          if (CmsStringUtil.isEmpty(getParamNewElement())) {
              validationErrors.append(messages.key(Messages.GUI_ELEM_RENAME_VALIDATE_ENTER_NEW_ELEM_0)).append("<br>");
          }
          if (!isValidElement(getParamNewElement())) {
              validationErrors.append(
                  messages.key(
                      Messages.GUI_ELEM_RENAME_VALIDATE_INVALID_NEW_ELEM_2,
                      getParamNewElement(),
                      getParamTemplate())).append("<br>");
          }
  
          setErrorMessage(validationErrors.toString());
      }
docs: Does validate the request parameters and returns a buffer with error messages.<p>
  
  If there were no error messages, the buffer is empty.<p>