/*首先写一个权限过滤filter*/
import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.FilterChain;
import java.io.IOException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletResponse;

public class RightFilter
     implements Filter {
   public void init(FilterConfig filterConfig) throws ServletException {
   }

   public void doFilter(ServletRequest request, ServletResponse response,
                        FilterChain chain) throws IOException, ServletException {
     HttpServletRequest req = (HttpServletRequest) request;
     HttpServletResponse res = (HttpServletResponse) response;
    
     HttpSession session = req.getSession(true);

     //从session里取的用户名信息
     String username = (String) session.getAttribute("username");
    
     //判断如果没有取到用户信息,就跳转到登陆页面
     if (username == null || "".equals(username)) {
       //跳转到登陆页面
       res.sendRedirect("http://"+req.getHeader("Host")+"/login.jsp");
     }
     else {
       //已经登陆,继续此次请求
       chain.doFilter(request,response);
     }
   }

   public void destroy() {
   }
}

下面配置这个过滤器
然后在web.xml里配置那些JSP文件需要登陆权限验证:

1.如果是某个具体的JSP文件(如a.jsp)需要登陆验证
<web-app>
   ...
   <filter>
     <filter-name>right</filter-name>
     <filter-class>com.taihuatalk.taihua.common.common.RightFilter</filter-class>
   </filter>

   <filter-mapping>
     <filter-name>right</filter-name>
     <url-pattern>/a.jsp</url-pattern>
   </filter-mapping>
   ...
</web-app>

2.如果是某一个目录(如a/目录)整个目录下的文件都需要登陆验证:
<web-app>
   ...
   <filter>
     <filter-name>right</filter-name>
     <filter-class>com.taihuatalk.taihua.common.common.RightFilter</filter-class>
   </filter>

   <filter-mapping>
     <filter-name>right</filter-name>
     <url-pattern>/a/*</url-pattern>
   </filter-mapping>
   ...
</web-app>

 


本文来源：http://blog.csdn.net/lhypang2006/archive/2007/06/24/1664714.aspx