一个检测是否登录过滤器例子

代码如下：

 

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<p> 
* 配置参数<p> 
* checkSessionKey 需检查的在 Session 中保存的关键字<br/> 
* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath<br/> 
* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath<br/> 
*/ 
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()); 
    } 
   } 
} 
}