public class LoginServlet extends HttpServlet {

    /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     * @throws java.lang.ClassNotFoundException
     * @throws TDA.ListaException
     */


    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException, ClassNotFoundException, ListaException {
        response.setContentType("text/html;charset=UTF-8");
        try (PrintWriter out = response.getWriter()) {
            /* TODO output your page here. You may use following sample code. */
            UserFile userF = new UserFile();
            String email = request.getParameter("email");
            String pass = request.getParameter("pwd");
            if (email != null) {
                if (userF.validarUsuario(email, pass)) {
                    HttpSession sesion = request.getSession(true);
                    sesion.setAttribute("usuario", email);
                    response.sendRedirect("inicio.htm");
                } else {
                    out.println("<h2>Fall&oacute; el inicio de sisi&oacuten</h2>");
                }
            }
        }
    }

    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /**
     * Handles the HTTP <code>GET</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try {
            processRequest(request, response);
        } catch (ClassNotFoundException | ListaException ex) {
            Logger.getLogger(LoginServlet.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    /**
     * Handles the HTTP <code>POST</code> method.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        try {
            processRequest(request, response);
        } catch (ClassNotFoundException | ListaException ex) {
            Logger.getLogger(LoginServlet.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    /**
     * Returns a short description of the servlet.
     *
     * @return a String containing servlet description
     */
    @Override
    public String getServletInfo() {
        return "Short description";
    }// </editor-fold>

}

public boolean validarUsuario(String correo, String pass) throws IOException, ClassNotFoundException, ListaException {
        File file = new File("./UserData.dat");
        ListaEnlazada listaE = readUser(file);
        UserInfo user;
        boolean correcto = false;

        for (int i = 1; i <= listaE.getSize(); i++) {
            user = (UserInfo) listaE.getNodo(i).elemento;
            if (user.getCorreo().equals(correo) && user.getPass().equals(pass)) {
                correcto = true;
            }
        }
        return correcto;
    }

public ListaEnlazada readUser(File file) throws IOException, ClassNotFoundException {
        ListaEnlazada listaE = new ListaEnlazada();
        //Valida si el archivo existe
        if (file.exists()) {
            try ( //Lee el archivo
                    ObjectInputStream objectInput = new ObjectInputStream(new FileInputStream(file))) {
                Object listTemp = objectInput.readObject();
                //casting del objeto
                listaE = (ListaEnlazada) listTemp;
                objectInput.close();
            }
        }
        return listaE;
    }