Java Web 串口通讯出现问题

有没有什么办法先执行完voltageDao.Volt(); 然后再去执行tempDao.Tempe();。因为我向同一个串口发送两条指令 并返回数据。但是按顺序发送只能接受到一个指令返回的数据。

 public class VolTemServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    TempDao tempDao = new TempDao();
    VoltageDao voltageDao = new VoltageDao();
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            voltageDao.Volt();
            request.setAttribute("Voltage", voltageDao.Voltage);
            request.setAttribute("current", voltageDao.current);
            tempDao.Tempe();        
            request.setAttribute("Temperature", tempDao.Temperature);
            request.setAttribute("Humidity", tempDao.Humidity);
            request.getRequestDispatcher("/NewFile.jsp").forward(request, response);

    }