1 public class LoginFilter implements Filter {
2 public void destroy() {
3
4 }
5
6 public void doFilter(ServletRequest request, ServletResponse response,
7 FilterChain chain) throws IOException, ServletException {
8 /*
9 * 1. 获取session中的user
10 * 2. 判断是否为null
11 * > 如果为null：保存错误信息，转发到msg.jsp
12 * > 如果不为null：放行
13 */
14 HttpServletRequest req = (HttpServletRequest) request;
15 Object user = req.getSession().getAttribute("sessionUser");
16 if(user == null) {
17 req.setAttribute("code", "error");//为了显示X图片
18 req.setAttribute("msg", "您还没有登录，请先登录");
19 req.getRequestDispatcher("你要跳转的登陆页面").forward(req, response);
20 } else {
21 chain.doFilter(request, response);//放行
22 }
23 }
24
25 public void init(FilterConfig fConfig) throws ServletException {
26
27 }
28 }
web.xml配置如下
<filter>
<display-name>LoginFilter</display-name>
<filter-name>LoginFilter</filter-name>
<filter-class>过滤器类路径</filter-class>
</filter>
<filter-mapping>
<filter-name>LoginFilter</filter-name>
<url-pattern>你要过滤的页面</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>LoginFilter</filter-name>
<servlet-name>你要过滤的servlet</servlet-name>
</filter-mapping>
</filter-mapping>