public void onMessage(String message) {
        try {
            NutMap msg = Json.fromJson(NutMap.class, message);
            String action = msg.getString("action");
            if (Strings.isBlank(action))
                return;
            String room = msg.getString("room");
            switch (action) {
            case "join":
                join(room);
                break;
            case "left":
                left(room);
                break;
            default:
                break;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    public void join(String room) {
        if (!Strings.isBlank(room)) {
            log.debugf("session(id=%s) join room(name=%s)", uu32, room);
            try (Jedis jedis = jedisPool.getResource()) {
                rooms.add(room);
                jedis.hset(NutzbookWebsocket.prefix+room, uu32, "");
            }
        }
    }

这些代码的作用，装入redis中，然后可以通知在线的用户吗

if (Notification.permission == "denied") {
		return;
	}

这个权限被denied是什么意思，没有什么权限？