关于Filter进行限制访问的问题！(语言-java)

Question

1. 问题：
   （1）想要的效果：
   在过滤器中，进行简单的限制访问。
   使用request.getRequestURI()获取链接，在登录servlet中，当用户输入账号密码点击登录按钮后，使用session存储user、用户名键值对，随后在跳转至主页面；当链接不是以login.jsp结尾且session存储的user为null，则跳转至登录界面login.jsp。
   （2）出现的问题：
   当跳转至登录页面点击登录后，提示如下错误。

2. 问题相关代码：
   （1）过滤器：

@WebFilter(urlPatterns = "/*")
public class WebFilter1 implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {}

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)servletRequest;
        HttpServletResponse response = (HttpServletResponse)servletResponse;
        HttpSession session = request.getSession();
        //限制访问
        String requestURI = request.getRequestURI();
        Object user = session.getAttribute("user");
        if((!requestURI.endsWith("login.jsp")) && user==null){
            response.sendRedirect("/login.jsp");
        }

        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {}
}

（2）登录页面对应servlet：

@WebServlet(urlPatterns = "/login")
public class LoginServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String userName = req.getParameter("userName");
        String password = req.getParameter("password");

        UsersService usersService = new UsersServiceImpl();
        Users users = usersService.loginResult(userName, password);

        resp.setContentType("text/html;charset=utf-8");
        if(users == null){
            PrintWriter writer = resp.getWriter();
            writer.println("<script>location.href='login.jsp';alert('用户名或密码不正确')</script>");
        }else{
            HttpSession session = req.getSession();
            session.setAttribute("user",users);  
            resp.sendRedirect("index.jsp");
        }
    }
}

1. 报错内容 ：