<dependency>  
        <groupId>org.springframework.boot</groupId>  
        <artifactId>spring-boot-starter-websocket</artifactId>  
    </dependency> 

public class WebsocketUtil {
  /**
   * 記錄當前在線的Session
   */
  private static final Map<String, Session> ONLINE_SESSION = new ConcurrentHashMap<>();

  /**
   * 添加session
   * @param userId
   * @param session
   */
  public static void addSession(String userId, Session session){
    // 此處只允許一個用戶的session鏈接。一個用戶的多個連接，我們視為無效。
    ONLINE_SESSION.putIfAbsent ( userId, session );
  }

  /**
   * 關閉session
   * @param userId
   */
  public static void removeSession(String userId){
    ONLINE_SESSION.remove ( userId );
  }

  /**
   * 給單個用戶推送消息
   * @param session
   * @param message
   */
  public static void sendMessage(Session session, String message){
    if(session == null){
      return;
    }
    // 同步
    RemoteEndpoint.Async async = session.getAsyncRemote ();
    async.sendText ( message );
  }

  /**
   * 向所有在線人發(fā)送消息
   * @param message
   */
  public static void sendMessageForAll(String message) {
    //jdk8 新方法
    ONLINE_SESSION.forEach((sessionId, session) -> sendMessage(session, message));
  }
}

/**
 * websocket接口處理類
 */
@Component
@ServerEndpoint(value = "/chat/{userId}")
public class WebsocketController {
    /**
     * 連接事件，加入注解
     * @param userId
     * @param session
     */
    @OnOpen
    public void onOpen(@PathParam(value = "userId") String userId, Session session) {
        String message = "[" + userId + "]加入聊天室！！";
        // 添加到session的映射關系中
        WebsocketUtil.addSession(userId, session);
        // 廣播通知，某用戶上線了
//        WebsocketUtil.sendMessageForAll(message);
    }

    /**
     * 連接事件，加入注解
     * 用戶斷開鏈接
     *
     * @param userId
     * @param session
     */
    @OnClose
    public void onClose(@PathParam(value = "userId") String userId, Session session) {
        String message = "[" + userId + "]退出了聊天室...";
        // 刪除映射關系
        WebsocketUtil.removeSession(userId);
        // 廣播通知，用戶下線了
        WebsocketUtil.sendMessageForAll(message);
    }

    /**
     * 當接收到用戶上傳的消息
     *
     * @param userId
     * @param session
     */
    @OnMessage
    public void onMessage(@PathParam(value = "userId") String userId, Session session, String message) {
        String msg = "[" + userId + "]:" + message;
        System.out.println("接收到信息：" + msg);
        // 直接廣播
        WebsocketUtil.sendMessageForAll(msg);
    }

    /**
     * 處理用戶活連接異常
     *
     * @param session
     * @param throwable
     */
    @OnError
    public void onError(Session session, Throwable throwable) {
        try {
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        throwable.printStackTrace();
    }
}

@PostMapping("/send")
public void send(@RequestParam("id")  String id,@RequestParam("message")String message) {
    Session session = ONLINE_SESSION.get(id);
    WebsocketUtil.sendMessage(session,message);
    System.out.println("發(fā)送成功");
}

/**
 *AppUtils類
 *
 * @author qiancj
 * @since 2020-06-30 13:02
 */
@Component("appUtils")
public class AppUtils {

    /**
     * 應用上下文
     */
    private static ApplicationContext context;

    @Resource
    public void setApplicationContext(ApplicationContext c) {
        context = c;
    }

    /**
     * 獲取配置參數(shù)
     *
     * @param property 配置參數(shù)名
     * @return 配置參數(shù)值
     */
    public static String getProperty(String property) {
        return context.getEnvironment().getProperty(property);
    }

    /**
     * 獲取bean對象
     *
     * @param requiredType Class
     * @param <T>          T
     * @return bean對象
     */
    public static <T> T getBean(Class<T> requiredType) {
        return context.getBean(requiredType);
    }

    /**
     * 獲取bean對象
     *
     * @param name         bean name
     * @param requiredType Class
     * @param <T>          T
     * @return bean對象
     */
    public static <T> T getBean(String name, Class<T> requiredType) {
        return context.getBean(requiredType);
    }

}

MessageService messageService = AppUtils.getBean(MessageService.class);