springMVC继承了spring的servletcontext上下文，
所以， controller里的@Resource注入可以用以下替代
@Resource
private IUserService userService;
替代：
WebApplicationContext ac1 = WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext());
WebApplicationContext ac2 = RequestContextUtils.getWebApplicationContext(request);
//IUserService userService = (IUserService)ac1.getBean("userService");
IUserService userService = (IUserService)ac2.getBean("userService");
List<User> users = userService.getAllUser();
request.setAttribute("users", users);