java - 使用 Spring Scheduler(Vaadin Chat 和 Spring Boot)

Question

我使用 Spring Boot 创建了 Vaadin Chat。我写了一个调度程序，我无法向其中添加功能。我需要从 MySQL 数据库中获取所有消息，其 ID 大于我们从最后一条消息中获取的 ID。

我的调度程序

  @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")));
        }



    }

这个调度程序正在上课 - Mainview

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());
        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")));
        }



    }

存储库

@Query(value = "SELECT * FROM chatMessages WHERE id > :id", nativeQuery = true)
    List<Message> getUnreadById(@Param("id") long id);

Answer 1

我可以在你的示例中发现至少两个问题，但我不能确定这些是唯一的问题

第一个问题是您将消息添加到新创建的 MessageList 实例中，但该实例并未在任何地方使用。这就像在一张纸上写下笔记，然后立即将纸扔进垃圾桶。相反，您需要存储对已添加为子组件的 MessageList 实例的引用，并向该实例添加新消息。

下一个问题是 @Scheduled 将在后台线程中运行，而 Vaadin 组件的更新只有在处理来自用户浏览器的请求时完成，才会自动反射(reflect)在浏览器中，例如当用户单击按钮时。要解决此问题，您需要启用 @Push 并且在更新组件时需要使用 access 方法，以便 Vaadin 可以防止多个线程互相踩踏并知道何时需要推出更改。请参阅https://vaadin.com/docs/v14/flow/advanced/tutorial-push-access.html有关此主题的更多信息。