Session在Filter中无效，求解！该如何解决

package com.zoe.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class LoginFilter implements Filter{    public void destroy() {        // TODO Auto-generated method stub            }    public void doFilter(ServletRequest req, ServletResponse res,            FilterChain chain) throws IOException, ServletException {        // TODO Auto-generated method stub        HttpServletRequest request = (HttpServletRequest) req;        HttpServletResponse response = (HttpServletResponse) res;        request.setCharacterEncoding("utf-8");        HttpSession session = request.getSession();        //session.setAttribute("name", "s");        System.out.println(session.getAttribute("name"));        if(session.getAttribute("name")!=null){            chain.doFilter(req, res);        }else{            request.getRequestDispatcher("../login.jsp").forward(req, res);        }    }    public void init(FilterConfig arg0) throws ServletException {        // TODO Auto-generated method stub            }}

package com.zoe.servlet;import java.io.IOException;import java.io.PrintWriter;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;import com.zoe.dao.UserDao;import com.zoe.entity.User;public class LoginServlet extends HttpServlet {    /**     * The doGet method of the servlet. <br>     *     * This method is called when a form has its tag value method equals to get.     *      * @param request the request send by the client to the server     * @param response the response send by the server to the client     * @throws ServletException if an error occurred     * @throws IOException if an error occurred     */    public void doGet(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        this.doPost(request, response);    }    /**     * The doPost method of the servlet. <br>     *     * This method is called when a form has its tag value method equals to post.     *      * @param request the request send by the client to the server     * @param response the response send by the server to the client     * @throws ServletException if an error occurred     * @throws IOException if an error occurred     */    public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        request.setCharacterEncoding("utf-8");        response.setContentType("text/html;charset=utf-8");        PrintWriter out = response.getWriter();        String name = request.getParameter("name");        String pwd = request.getParameter("pwd");        User u = new User();        u.setName(name);        u.setPwd(pwd);        HttpSession session = request.getSession();        boolean flag = new UserDao().login(u);        if(flag){            session.setAttribute("name", name);            request.getRequestDispatcher("admin/admin.jsp").forward(request, response);        }else{            response.sendRedirect("error.jsp");        }        out.close();    }}