public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)

            throws IOException, ServletException {

        //转换类型

        HttpServletRequest req=(HttpServletRequest) request;

        HttpServletResponse res=(HttpServletResponse) response;

        //获取请求界面的路径

        String a=req.getRequestURI();

        if(a.contains(".css") || a.contains(".js") || a.contains(".png")|| a.contains(".jpg")){

            //如果发现是css或者js文件，直接放行

               chain.doFilter(request, response);

            }

         //在else中放对网页过滤的代码

        else{}    }