session监听器怎样得到request和response

public class SessionTimeout implements Filter{
   RequestDispatcher rd = null;

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

   // New Session so forward to login.jsp
   //因为前面一个Session已经失效，如果还在这个站点，必然是新创立的Session
   if (session.isNew()){
     requestDispatcher = request.getRequestDispatcher("/login/login.jsp");
     requestDispatcher.forward(request, response);
  }

  // Not a new session so continue to the requested resource
   else{
      filterChain.doFilter(request, response);
  }
}

public void init(filterConfig arg) throws ServletException{}
public void destroy(){}

}
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