WEB.XML 

       
         
      
       userSessionKey
          
      
       USERSESSIONKEY
        
       
       
         
      
       rediretPage
          
      
       /u_member/Login.jsp
        
       
       
         
      
       uncheckUrls
          
      
       /u_member/insert.jsp,/u_member/Login.jsp
        
     

Filter 过滤器代码

package go.onlineShop.filter;import java.io.IOException;import java.util.Arrays;import java.util.List;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.annotation.WebFilter;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet Filter implementation class IsLoginFilter * 推断是否登陆过滤器 */@WebFilter("/u_member")public class IsLoginFilter implements Filter {	//从xml中取值	String uncheckUrls =null;	String userSessionKey=null;	String rediretPage=null;    /**     * Default constructor.      */    public IsLoginFilter() {        // TODO Auto-generated constructor stub    }	/**	 * @see Filter#destroy()	 */	public void destroy() {		// TODO Auto-generated method stub	}	/**	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)	 */	public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {		// TODO Auto-generated method stub		//1.得到訪问路径		HttpServletRequest request = (HttpServletRequest)req;		HttpServletResponse response = (HttpServletResponse)res;		String reqUrl = request.getRequestURL().toString();		String reqURI = request.getRequestURI();				String servletPath = request.getServletPath();			//	String[] uncheckUrl = uncheckUrls.split(",");		List
     
       urls = Arrays.asList(uncheckUrls.split(","));		//2.假设是属于不须要过滤的地址就直接  放行  方法结束		if(urls.contains(servletPath)){			chain.doFilter(request, response);			return;		}				//3.从session中获取sessionKey相应的值。若不存在  则跳转到登陆页面				Object user = request.getSession().getAttribute(userSessionKey);		if(user==null){			request.getRequestDispatcher(rediretPage).forward(request, response);			return;		}		//4若存在 则放行；		chain.doFilter(request, response);	}	/**	 * @see Filter#init(FilterConfig)	 */	public void init(FilterConfig fConfig) throws ServletException {		rediretPage=fConfig.getServletContext().getInitParameter("rediretPage");		uncheckUrls=fConfig.getServletContext().getInitParameter("uncheckUrls");		userSessionKey=fConfig.getServletContext().getInitParameter("userSessionKey");	}}
     

Login页面