package cn.hongxin.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 init(FilterConfig filterConfig) throws ServletException { } public void doFilter(ServletRequest request, ServletResponse response,  FilterChain chain) throws IOException, ServletException { //將request強轉成htt... HttpServletRequest req = (HttpServletRequest) request; //獲取session HttpSession ss = req.getSession(); //從session中獲取user if(ss.getAttribute("user")==null){  System.err.println("你還沒有登錄");  req.getSession().setAttribute("msg", "請你先登錄");  //重定向到登錄  HttpServletResponse resp = (HttpServletResponse) response;  resp.sendRedirect(req.getContextPath()+"/index.jsp");[W2]  }else{  //放行  chain.doFilter(request, response); } } public void destroy() { }}

<filter> <filter-name>login</filter-name> <filter-class>cn.itcast.filter.LoginFilter</filter-class> </filter> <filter-mapping> <filter-name>login</filter-name> <url-pattern>/jsps/*</url-pattern> <url-pattern>/views/*</url-pattern> </filter-mapping>