SpringBoot and Mybatis-plus andWebsocket Qusetion

Question

When I create a connection via websocket, I want to find the user's information from the database and store it in "friendsList" but when I call "getUserByUid" via "userMapper", it gives me null. enter image description here "CKt3z2RW6s" is uid.

I tried to put "userMapper.getUserByUid()" in another method, and receive it through the User object. This is my code

package com.chat.imbackend.controller;


import com.alibaba.fastjson.JSON;
import com.chat.imbackend.entity.Friends;
import com.chat.imbackend.entity.Messages;
import com.chat.imbackend.entity.User;
import com.chat.imbackend.mapper.UserMapper;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.RestController;

import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;


@Slf4j
@Component
@CrossOrigin
@RestController
@ServerEndpoint(value = "/websocket/{uid}")
public class WebSocketController {
    private Session session;


    @Autowired
    private UserMapper userMapper;

    /**
     * 好友列表
     */
    public static List<Friends> friendsList = new ArrayList<>();

    /**
     * 定义并发HashMap存储好友WebSocket集合
     */
    public static ConcurrentHashMap<String, WebSocketController> webSocketSession = new ConcurrentHashMap<>();

    @OnOpen
    public void onOpen(@PathParam(value = "uid") String uid, Session session) {
        // 设置session
        this.session = session;
        // Put添加当前类
        webSocketSession.put(uid, this);
        try {
            System.out.println(uid);
            User user = userMapper.getUserByUid(uid);
            // Add添加当前好友信息
            friendsList.add(Friends.builder().uid(uid).nickname(user.getNickname()).avatar(user.getAvatar()).build());
            // 通知更新好友信息列表
            updateFriendInformationList();

            log.info("【WebSocket消息】有新的连接[{}], 连接总数:{}", uid, webSocketSession.size());

        }catch(Exception e){
            log.error(e.getMessage());
        }
    }

    /**
     * 通知更新好友信息列表
     */
    private synchronized void updateFriendInformationList() {
        webSocketSession.forEach((key, val) -> {
            // 初始化存储属于自己的好友列表 排除自己
            List<Friends> friends = new ArrayList<>();
            // 迭代所有好友列表
            friendsList.forEach((friend) -> {
                // 在 所有好友信息列表 中验证非自己
                if (!friend.getUid().equals(key)) {
                    // 追加非自己的好友信息
                    friends.add(friend);
                }
            });
            // 发送消息
            sendP2PMessage(key, JSON.toJSONString(Messages.builder().type("updateFriendsList").receiveUid(key).messages(friends).build()));
        });
    }

    @OnMessage
    public void onMessage(@PathParam(value = "uid") String uid, String message) {
        log.info("【WebSocket消息】 收到客户端[{}] 发送消息:{} 连接总数:{}", uid, message, webSocketSession.size());

        // 验证消息内容
        if (StringUtils.hasLength(message)) {
            try {
                // 消息内容转消息对象
                Messages messages = JSON.parseObject(message, Messages.class);
                // 发送消息
                sendP2PMessage(messages.getReceiveUid(), message);
            } catch (Exception e) {
                log.error("WebSocket消息异常:", e);
            }
        }
    }

    @OnClose
    public void onClose(@PathParam(value = "uid") String uid) {
        friendsList.remove(friendsList.stream().filter((friends -> friends.getUid().equals(uid))).findAny().orElse(null));
        webSocketSession.remove(uid);
        // 通知更新好友信息列表
        updateFriendInformationList();
        log.info("【WebSocket消息】客户端[{}]连接断开, 剩余连接总数:{}", uid, webSocketSession.size());
    }

    /**
     * 点对点发送
     */
    public static synchronized void sendP2PMessage(String uid, String message) {
        log.info("【WebSocket消息】点对点发送消息, uid={} , message={}", uid, message);
        try {
            webSocketSession.get(uid).session.getBasicRemote().sendText(message);
        } catch (IOException e) {
            log.error("点对点发送异常:", e);
        }
    }


}

package com.chat.imbackend.entity;


import com.baomidou.mybatisplus.annotation.*;
import lombok.Data;
import java.util.Date;

@Data
@TableName("tbl_users")
public class User {

    @TableId(type = IdType.AUTO)
    Integer id;

    String uid;

    String nickname;

    String password;

    String avatar = "src/assets/Resource/avatar/defaultAvatar.png";

    @TableField(fill = FieldFill.INSERT)
    Date jtime;


}

package com.chat.imbackend.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.chat.imbackend.entity.User;
import org.apache.ibatis.annotations.*;


@Mapper
public interface UserMapper extends BaseMapper<User> {

    @Select("select * from tbl_users where uid= #{uid}")
    User getUserByUid(@Param("uid") String uid);



    @Update("UPDATE tbl_users SET nickname = #{nickname} WHERE uid = #{uid}")
    void modifyUser(@Param("uid") String uid, @Param("nickname") String nickname);

    @Update("UPDATE tbl_users SET avatar = #{avatar} WHERE uid = #{uid}")
    void modifyAvatar(@Param("uid") String uid, @Param("avatar") String avatar);

}

enter image description here

I found this. My userMapper in this class is null. Why?

enter image description here