final List<VaMessenger<FessMessages>> errorMessages = new ArrayList<>();
        AdminSearchlistAction.validateFields(doc, errorMessages::add);

        assertFalse(errorMessages.isEmpty());

        // Verify error messages use field names without doc. prefix
        final FessMessages messages = new FessMessages();
        errorMessages.forEach(m -> m.message(messages));

    @Override
    public ActionValidator<FessMessages> createValidator() {
        return systemHelper.createValidator(requestManager, this::createMessages, myValidationGroups());
    }

    /**
     * Creates a new messages instance for handling validation and user messages.
     * This method can be called by the application to create message containers.
     *
     * @return a new FessMessages instance
     */
    @Override

src/main/resources/
├── fess_config.properties     # Main configuration
├── app.xml, fess.xml          # DI configuration
├── fess_*.xml                 # Feature-specific DI
├── fess_label_*.properties    # UI labels (i18n)
├── fess_message_*.properties  # Validation messages (i18n)
└── fess_indices/              # OpenSearch index mappings

src/main/webapp/WEB-INF/view/  # JSP templates
src/test/java/.../it/          # Integration tests (*Tests.java)
```

     * @return concatenated string of localized validation messages separated by spaces
     */
    protected String getMessage(final VaMessenger<FessMessages> validationMessagesLambda) {
        final FessMessages messages = new FessMessages();
        validationMessagesLambda.message(messages);
        return messageManager.toMessageList(request.getLocale() == null ? Locale.ENGLISH : request.getLocale(), messages)

     * Adds a password validation error message to the messages object based on the error key.
     *
     * @param messages the FessMessages object to add the error to
     * @param errorKey the error key identifying the type of password validation error
     */
    protected void addPasswordValidationError(final FessMessages messages, final String errorKey) {
        switch (errorKey) {
        case "errors.password_length":

         * @return This ApiErrorResponse instance.
         */
        public ApiErrorResponse message(final VaMessenger<FessMessages> validationMessagesLambda) {
            final FessMessages messages = new FessMessages();
            validationMessagesLambda.message(messages);
            message = ComponentUtil.getMessageManager()

     * Adds a password validation error message to the messages object based on the error key.
     *
     * @param messages the FessMessages object to add the error to
     * @param errorKey the error key identifying the type of password validation error
     */
    protected void addPasswordValidationError(final FessMessages messages, final String errorKey) {
        switch (errorKey) {
        case "errors.password_length":

import org.codelibs.fess.app.service.GroupService;
import org.codelibs.fess.app.web.CrudMode;
import org.codelibs.fess.app.web.base.FessAdminAction;
import org.codelibs.fess.mylasta.action.FessMessages;
import org.codelibs.fess.opensearch.user.exentity.Group;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalEntity;

     * Adds a password validation error message to the messages object based on the error key.
     *
     * @param messages the FessMessages object to add the error to
     * @param errorKey the error key identifying the type of password validation error
     */
    protected void addPasswordValidationError(final FessMessages messages, final String errorKey) {
        switch (errorKey) {
        case "errors.password_length":

     * @param runtimeGroups   The runtime groups.
     * @return A new action validator.
     */
    public ActionValidator<FessMessages> createValidator(final RequestManager requestManager,
            final UserMessagesCreator<FessMessages> messagesCreator, final Class<?>[] runtimeGroups) {
        return new FessActionValidator<>(requestManager, messagesCreator, runtimeGroups);
    }

    /**