检测用户是否登陆的过滤器

Java code

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import javax.servlet.*;    
import javax.servlet.http.HttpServletRequest;    
import javax.servlet.http.HttpServletResponse;    
import javax.servlet.http.HttpSession;    
import java.util.List;    
import java.util.ArrayList;    
import java.util.StringTokenizer;    
import java.io.IOException;    
   
/**   
* 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面    


* 配置参数    


* checkSessionKey 需检查的在 Session 中保存的关键字   

* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath   

* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath   

*/   
public class CheckLoginFilter    
implements Filter    
{    
      protected FilterConfig filterConfig = null;    
      private String redirectURL = null;    
      private List notCheckURLList = new ArrayList();    
      private String sessionKey = null;    

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException    

{    
    HttpServletRequest request = (HttpServletRequest) servletRequest;    
    HttpServletResponse response = (HttpServletResponse) servletResponse;    
   
     HttpSession session = request.getSession();    
    if(sessionKey == null)    
    {    
     filterChain.doFilter(request, response);    
     return;    
    }    
    if((!checkRequestURIIntNotFilterList(request)) && session.getAttribute(sessionKey) == null)    
    {    
     response.sendRedirect(request.getContextPath() + redirectURL);    
     return;    
    }    
    filterChain.doFilter(servletRequest, servletResponse);    
}    
   
public void destroy()    
{    
    notCheckURLList.clear();    
}    
   
private boolean checkRequestURIIntNotFilterList(HttpServletRequest request)    
{    
    String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo());    
    return notCheckURLList.contains(uri);    
}    
   
public void init(FilterConfig filterConfig) throws ServletException    
{    
    this.filterConfig = filterConfig;    
    redirectURL = filterConfig.getInitParameter("redirectURL");    
    sessionKey = filterConfig.getInitParameter("checkSessionKey");    
   
    String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList");    
   
    if(notCheckURLListStr != null)    
    {    
     StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");    
     notCheckURLList.clear();    
     while(st.hasMoreTokens())    
     {   

   notCheckURLList.add(st.nextToken());    
     }    
    }    
}    
}