第一次使用过滤器

<filter>
  <filter-name>过滤器的名字</filter-name>
  <filter-class>   
   过滤器的路径（servlet）
  </filter-class>

<init—param>  

　　<param—name>RejectedlP<／param-name>／／过滤器初始化参数名RejectedlP  

　　<param-value>192.168.12.*／param-value>  

<／init—pamm> 
 </filter>
 <filter-mapping>
  <filter-name>必须和上面的过滤器名字一致</filter-name>
  <url-patter>/course.htm</url-pattern><!-- 访问哪些页面或者跳转的文件 -->
 </filter-mapping>

public class CourseCheckFilter implements Filter {  

private Logger log=Logger.getLogger(this.getClass());

 public void destroy()  {  }

 @Override

public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain chain) throws IOException, ServletException {
  HttpServletResponse res=(HttpServletResponse)response;
  HttpServletRequest req=(HttpServletRequest)request;
  if(req.getRequestURI().endsWith("course.htm")==false)//只对course.htm文件过滤
  {
   chain.doFilter(request,response);//通过不处理
   return;
  }
  String requestURL=req.getRequestURL().toString();
  String strParam=req.getQueryString();
  if(strParam!=null&&strParam.length()>0)
  {
   requestURL=requestURL+"?"+strParam;
  }
  String SSO_URL="warn.htm?"+strParam
  if(check(req,res)==false)
  {
   res.sendRedirect(SSO_URL);;//跳转到course.htm时不符合条件是跳转到该路径
   return;
  }
  chain.doFilter(request,response);  //通过不处理
 }

}