public class MySessionListener implements HttpSessionListener{
ProfileDAO instance = null;
ServletContext servletContext = null;
private int sessionCount;

public MySessionListener() {
    this.sessionCount = 0;
}
@Override
public void sessionCreated (HttpSessionEvent event) {
    synchronized (this) {
        sessionCount++;
    }
    DAOFactory daoFactory = new DAOFactory();
    try {
        instance = daoFactory.getProfileDAO();
    } catch (DAOException e) {
        e.printStackTrace();
    }
    servletContext = event.getSession().getServletContext();
    servletContext.setAttribute("instance", instance);
}
@Override
public void sessionDestroyed(HttpSessionEvent event) {
    synchronized (this) {
        --sessionCount;
    }
    try {
        instance.close();
    } catch (DAOException e) {
        e.printStackTrace();
    }
}}

public class Servlet extends HttpServlet {
HttpSession session = null;
PrintWriter out;
List<Profile> list;

    public void getHtmlPages (int namberPage) {...}


protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=utf-8");
    out = response.getWriter();
    String userName = request.getParameter("user_name");
    String nickName = request.getParameter("nick_name");
    String userMail = request.getParameter("user_mail");
    String password = request.getParameter("password");
    int id = Integer.parseInt(request.getParameter("id"));
    int index = Integer.parseInt(request.getParameter("index"));

    session = request.getSession();
    ProfileDAO instance = null;
    session.setAttribute("instance", instance);

    try {

        Profile profile = new Profile();
        profile.setUserName(userName);
        profile.setNickName(nickName);
        profile.setUserMail(userMail);
        profile.setPassword(password);
        profile.setId(id);
        switch (index) {
            case 1:
                list = instance.selectAllProfiles();
                getHtmlPages(1);
                break;
            case 2:
                instance.deleteProfile(profile);
                getHtmlPages(2);
                break;
            case 3:
                instance.updateProfile(profile);
                getHtmlPages(3);
                break;
            default:
                getHtmlPages(4);
                break;
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request,response);
}}