java - 以错误的顺序显示消息
问题描述
我创建了 vaadin 聊天,我需要当任何用户进入聊天时,他应该只能看到来自 MySQL 数据库的最后 10 条消息。我认为我的代码实现不正确。因为它向我显示了前 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 我有最后 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
解决方案
默认情况下,SQL 查询按升序排序。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();
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