/** 获取用户列表数据 */
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    // 设置编码-解决中文乱码
    resp.setCharacterEncoding("utf-8");

    UserService userService = new UserService();

    List<User> users = userService.getAllUser();

    Gson gson = new Gson();
    String userJson = gson.toJson(users); // 将List<User>集合中的User转换成json格式的字符串数据

    //		System.out.println(userJson);

    // 将json格式的用户列表返回的浏览器端
    PrintWriter out = resp.getWriter();
    out.write(userJson);
  }
  /** 处理登录请求 */
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    /** 用户服务 */
    UserService userService = new UserService();

    String username = (String) req.getParameter("username");
    String password = req.getParameter("password");

    User user = userService.login(username, password);

    if (user == null) { // 登录失败,跳转到登录页面
      req.setAttribute("error", "用户名或密码错误!");
      req.getRequestDispatcher("/login.jsp").forward(req, resp); // 请求转发

    } else { // 登录成功,跳转到成功页面
      // 登录成功,将用户信息放入session中
      HttpSession session = req.getSession();
      session.setAttribute("user", user);
      resp.sendRedirect(req.getContextPath() + "/users.jsp");
    }
  }