1、不使用過濾器實現，在需要攔截的頁面通過session判斷是否登陸，若沒登陸則跳轉到login.jsp頁面：

<% 
    Admin admin = (Admin)session.getAttribute("admin");
    if(admin == null){
         response.sendRedirect("login.jsp");
         return;
    }
%>

public class JspFilter implements Filter {
       public void destroy() {}
       public
 
 void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)  throws IOException, ServletException {        
             HttpServletRequest httpServletRequest = (HttpServletRequest)request;
             HttpServletResponse httpServletResponse = (HttpServletResponse) response;

             HttpSession session = httpServletRequest.getSession();
             Admin admin = (Admin)session.getAttribute("admin"
 
);

             String url = httpServletRequest.getRequestURI();

             //若不進行url.endsWith("login.jsp")判斷則會出現無限迴圈重定向的問題；
             //若登陸成功之後則admin不為null，繼續執行
             if(url.endsWith("login.jsp") || admin!=null){        
                    chain.doFilter(httpServletRequest, httpServletResponse);
                    return
 
;
             }

             //若該if放在上一if語句之前，仍然會出現無限迴圈重定向的問題
             if(admin==null){
                    httpServletResponse.sendRedirect("/bookStore/admin/login.jsp");
                    return;
             }
       }
       public void init(FilterConfig fConfig) throws ServletException {
       }
}

②web.xml

<filter>
     <filter-name>jspFilter</filter-name>
     <filter-class>com.zh.filter.JspFilter</filter-class>
</filter>
<filter-mapping>
     <filter-name>jspFilter</filter-name>
     <url-pattern>*.jsp</url-pattern>
</filter-mapping>

注意點:
Ⅰ、請求轉發url不會變，過濾器只過濾一次；
重定向url一直改變，過濾器會一直過濾，死迴圈
Ⅱ、當訪問JspFilter時，由於使用者沒有登陸，所以將跳轉到login.jsp,但在Filter同樣對login.jsp進行了過濾，所以當瀏覽器跳轉到login.jsp時，經驗證還是沒有登陸，那麼就會一直無限迴圈的進行跳轉，報錯。