package com.gavin.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class LoginFilter implements Filter {    public void destroy() {        // TODO Auto-generated method stub    }    public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException {        // TODO Auto-generated method stub        HttpServletResponse response = (HttpServletResponse) resp;        HttpServletRequest request = (HttpServletRequest) req;        HttpSession session = request.getSession(true);        String username = (String) session.getAttribute("username");//         String url = request.getRequestURI();        if (username == null || username.equals("")) {            // 判断获取的路径不为空且不是访问登录页面或执行登录操作时跳转            if (url != null && !url.equals("") && (url.indexOf("Login") < 0 && url.indexOf("login") < 0)) {                response.sendRedirect("login.jsp");                return;            }        }        // 已通过验证，用户访问继续        chain.doFilter(req, resp);    }    public void init(FilterConfig filterConfig) throws ServletException {        // TODO Auto-generated method stub    }}

 <filter>  <filter-name>loginFilter</filter-name>  <filter-class>com.gavin.filter.LoginFilter</filter-class> </filter> <filter-mapping>  <filter-name>loginFilter</filter-name>  <url-pattern>/*</url-pattern> </filter-mapping>