JSP :: Apache Tomcat 6 - Data Not Retrieved

I am developing an dashboard application in Java, JSTL, MySql, Apache Tomcat 6.I have the below files

1. Dashboard.java (model)
2. DashboardDAO.java (dao)
3. DashboardController.java (Controller)
//Source
protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
String forward = "";
forward = LIST_DASHBOARD;
HttpSession session = req.getSession(true);
session.setAttribute("dboard", dao.getAlldashboard(req));
setMasterInfo(req);
RequestDispatcher view = req.getRequestDispatcher(forward);
view.forward(req, res);

[code]....

It works in the first time. But, after sometime the data is not retrieved and display empty screen. Once, i stop and start the server again, the data is getting retrieved again. But, later when we refresh the empty page is getting displayed again.