protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String error = null;
String username = req.getParameter("username");
String password = req.getParameter("password");
Subject subject = SecurityUtils.getSubject();
UsernamePasswordToken token = new UsernamePasswordToken(username, password);
token.setRememberMe(true);
try {
subject.login(token);
} catch (UnknownAccountException e) {
error = "用户名/密码错误";
} catch (IncorrectCredentialsException e) {