<!--session过期filter -->
 <filter>
 <init-param>
  <param-name>exclusions</param-name>
  <param-value>/SarService</param-value>
 </init-param>
 <filter-name>loginFilter</filter-name>
 <filter-class>org.sigsit.vinca.sar.filter.LoginFilter
 </filter-class>
 </filter>
 <filter-mapping>
 <filter-name>loginFilter</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>

 public void doFilter(ServletRequest request, ServletResponse response, 
      FilterChain chain) throws IOException, ServletException { 
    // 由于 session 属于 HTTP 范畴，故需要向下转型成 HttpServletRequest 类型 
    HttpServletRequest req = (HttpServletRequest) request; 
    HttpServletResponse res=(HttpServletResponse)response;
     
    HttpSession session = req.getSession(); // 取得 session 
    
    String username = (String) session.getAttribute("username"); 
    StringBuffer fileURL = req.getRequestURL();

    if(fileURL.indexOf(this.exclusions)!=-1){
        chain.doFilter(request, response); 
    }
    else{
             //原来的处理代码
    }

  } 

 public void init(FilterConfig config) throws ServletException {
 // TODO Auto-generated method stub
 this.exclusions=config.getInitParameter("exclusions");
 }