java - 以错误的顺序显示消息

Question

我创建了 vaadin 聊天，我需要当任何用户进入聊天时，他应该只看到 MySQL 数据库中的最后 10 条消息。我认为我的代码执行不正确。因为它显示了前 10 条消息，尽管程序应该显示最后 10 条消息。

我的代码MainView 类 -

public class MainView extends VerticalLayout {
    private final MessagesInfoManager messagesInfoManager;
    private final RestService restService;
    private String username;
    private TextField textField;
    private Message messageLast;


    @Autowired
    public MainView(RestService restService) {
        this.messagesInfoManager = MessageConfigurator.getInstance().getChatMessagesInfoManager();
        addClassName("main-view");
        setSizeFull();
        setDefaultHorizontalComponentAlignment(Alignment.CENTER);

        H1 header = new H1("Vaadin Chat");
        header.getElement().getThemeList().add("dark");

        add(header);

        askUsername();
        this.restService = restService;
    }

    private void askUsername() {
        HorizontalLayout layout = new HorizontalLayout();
        TextField usernameField = new TextField();
        Button startButton = new Button("Start chat");

        layout.add(usernameField, startButton);

        startButton.addClickListener(click -> {
            username = usernameField.getValue();
            remove(layout);
            showChat(username);
        });

        add(layout);
    }

    private void showChat(String username) {
        MessageList messageList = new MessageList();

        List<Message> lasts = restService.getLast();
        for (Message message : lasts) {
            messageList.add(new Paragraph(message.getFromV() + ": " + message.getMessageV()));
        }

        messageLast = lasts.get(lasts.size() - 1);

        add(messageList, createInputLayout(username, messageList));
        expand(messageList);
    }

    private Component createInputLayout(String username, MessageList messageList) {
        HorizontalLayout layout = new HorizontalLayout();
        layout.setWidth("100%");

        TextField messageField = new TextField();
        messageField.addKeyDownListener(Key.ENTER, keyDownEvent -> sender(messageField, messageList));
        Button sendButton = new Button("Send");
        sendButton.addThemeVariants(ButtonVariant.LUMO_PRIMARY);

        layout.add(messageField, sendButton);
        layout.expand(messageField);

        messageField.addFocusListener(event -> {
            for (Message message : messagesInfoManager.getMessagesByUI(getUI())) {
                if (!message.getFromV().equals(username)) {
                    message.setUnread(false);
                    this.restService.updateMessage(message.getId(), message);
                }
            }
        });

        sendButton.addClickListener(click -> sender(messageField, messageList));
        messageField.focus();

        return layout;
    }

    private void sender(TextField textField, MessageList messageList) {
        Message message = new Message(username, textField.getValue());
        message = restService.saveMessage(message);
        messageLast = message;
        this.textField = textField;
        messagesInfoManager.updateMessageUIInfo(new MessageInfo(messageList, message, this));
        textField.clear();
        textField.focus();

    }

    @Scheduled(fixedDelay = 5000)
    public void scheduleFixedDelayTask() {

        MessageList messageList = new MessageList();

        List<LinkedHashMap> lasts = restService.getUnreadMessages(messageLast.getId());

        for (LinkedHashMap message : lasts) {
            messageList.add(new Paragraph(message.get("fromV") + ": " + message.get("messageV")));
        }

        messagesInfoManager.updateMessageUIInfo(new MessageInfo(messageList, messageLast, this));

    }

}

我有 api/last - 应该显示最后 10 条消息

 @GetMapping("/api/last")
    public List<Message> getLasts() {
        return (messageService.getLast());
    }

MessageRepository 我有最近 10 条消息的 SQL 查询

@Query(value = "SELECT * FROM chatMessages LIMIT 10", nativeQuery = true)
    List<Message> getLastMessages();

我的Github https://github.com/adk96/vaadin-chat

Answer 1

SQL 查询默认按升序排序。您需要将查询设置为按降序排序。

@Query(value = "SELECT * FROM chatMessages ORDER BY <yourFieldName> DESC LIMIT 10", nativeQuery = true)
    List<Message> getLastMessages();