@Override
      public void doFilter(ServletRequest request, ServletResponse response,
              FilterChain chain) throws IOException, ServletException {
    	   
          // 获得在下面代码中要用的request,response,session对象
          HttpServletRequest servletRequest = (HttpServletRequest) request;
           HttpServletResponse servletResponse = (HttpServletResponse) response;
           HttpSession session = servletRequest.getSession();
           // 获得用户请求的URI
           String path = servletRequest.getRequestURI();
           //System.out.println("PATH："+path);
           
           // 从session里取员工工号信息
          String empId = (String) session.getAttribute("username");
        
          System.out.println("当前用户："+empId);
           /*创建类Constants.java，里面写的是无需过滤的页面
           for (int i = 0; i < Constants.NoFilter_Pages.length; i++) {
               if (path.indexOf(Constants.NoFilter_Pages[i]) > -1) {
                   chain.doFilter(servletRequest, servletResponse);
                   return;
               }
           }*/
           
          // 登陆页面无需过滤
          if(path.indexOf("/login.jsp") > -1) {//访问的URL保护login.jsp,放行
        	  System.out.println("用户名为空，到登录界面");
              chain.doFilter(servletRequest, servletResponse);
          }else {//否则，就进入else
        	  if (empId == null || "".equals(empId)) {//没有登录，用户名为空
	              // 跳转到登陆页面
	        	  if(path.indexOf("/user/login")>-1) {//如果URL为用户提交的登录。放行
	        		  System.out.println("去登录");
	        		  chain.doFilter(request, response);
	        	  }else {//否则，强制跳转到login.jsp
	        		  System.out.println("之前木有登录");
	        		  servletResponse.sendRedirect(servletRequest.getContextPath()+"/jsp/login.jsp");
	        	  }
	           } else {//登录过了，用户名不为空。放行
	               chain.doFilter(request, response);
	           }
          }
         
       }