public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { // session属于http范畴,所以要将ServletRequest转换成httpServletRequest try { HttpServletRequest req = (HttpServletRequest) request; HttpSession session = req.getSession(); if (session.getAttribute("username") != null) { chain.doFilter(request, response); } else { request.getRequestDispatcher("error.jsp").forward(request, response); } } catch (RuntimeException e) { e.printStackTrace(); } }