验证登录过滤器类怎么配置web.xml

/** * 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面  * 配置参数  * checkSessionKey 需检查的在 Session 中保存的关键字 * redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath  * notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath */public class LoginFilter implements Filter {    protected FilterConfig filterConfig = null;    private String redirectURL = null;    private List notCheckURLList = new ArrayList();    private String sessionKey = null;    public void init(FilterConfig filterConfig) throws ServletException {        this.filterConfig = filterConfig;        redirectURL = filterConfig.getInitParameter("redirectURL");        sessionKey = filterConfig.getInitParameter("checkSessionKey");        String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList");        if (notCheckURLListStr != null) {            StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");            notCheckURLList.clear();            while (st.hasMoreTokens()) {                notCheckURLList.add(st.nextToken());            }        }    }    public void doFilter(ServletRequest servletRequest,            ServletResponse servletResponse, FilterChain filterChain)            throws IOException, ServletException {        HttpServletRequest request = (HttpServletRequest) servletRequest;        HttpServletResponse response = (HttpServletResponse) servletResponse;        HttpSession session = request.getSession();        if (sessionKey == null) {            filterChain.doFilter(request, response);            return;        }        if ((!checkRequestURIIntNotFilterList(request))                && session.getAttribute(sessionKey) == null) {            response.sendRedirect(request.getContextPath() + redirectURL);            return;        }        filterChain.doFilter(servletRequest, servletResponse);    }    public void destroy() {        notCheckURLList.clear();    }    private boolean checkRequestURIIntNotFilterList(HttpServletRequest request) {        String uri = request.getServletPath()                + (request.getPathInfo() == null ? "" : request.getPathInfo());        return notCheckURLList.contains(uri);    }}

    <filter>        <filter-name>Set Character Encoding</filter-name>        <filter-class>com.yj.util.CharacterEncodingFilter</filter-class>        <init-param>            <param-name>encoding</param-name>            <param-value>GBK</param-value>        </init-param>    </filter>