code: private boolean checkForRequired(final AjaxRequestTarget _target)
      {
          AjaxSubmitCloseButton.LOG.trace("entering checkForRequired");
          boolean ret = true;
          if (!(getForm().getParent().getDefaultModel() instanceof TableModel)) {
              final IRequestParameters parameters = getRequest().getRequestParameters();
              final List<FormPanel> panels = getFormPanels();
              for (final FormPanel panel : panels) {
                  for (final Entry<String, Label> entry : panel.getRequiredComponents().entrySet()) {
                      final StringValue value = parameters.getParameterValue(entry.getKey());
                      if (value.isNull() || value.isEmpty()) {
                          final Label label = entry.getValue();
                          label.add(AttributeModifier.replace("class", "eFapsFormLabelRequiredForce"));
                          _target.add(label);
                          ret = false;
                      }
                  }
              }
              if (!ret) {
                  showDialog(_target, "MandatoryDialog", false, false);
              }
          }
          return ret;
      }
docs: Method checking if the mandatory field of the Form are filled with a value,
  and if not opens a WarnDialog and marks the fields in the Form via Ajax.
  
  @param _target RequestTarget used for this Request
  @return true if all mandatory fields are filled, else false