Filter 问题，我要通过 Filter 做一个1分钟内限制请求次数的程序

我要通过 Filter 做一个1分钟内限制请求次数的程序。基本思想是这样，先记录一个开始时间，

当请求过来时先判断时间是否已经过了你要求的时间，计数器清零，然后在++，如果没有过那么

就直接判断是否已过了你要求的数目上限。下边是已经完成的程序，高手补充下，谢谢。
public class SessionSingleFilter implements Filter {

private static final Logger LOG = Logger.getLogger(SessionSingleFilter.class);

public void init(FilterConfig filterConfig) throws ServletException {
}

public void doFilter(ServletRequest servletRequest, ServletResponse

servletResponse, FilterChain filterChain)
throws IOException, ServletException {
filterChain.doFilter(servletRequest, servletResponse);
System.out.println("Filter66");

Calendar c =Calendar.getInstance();
Date date = c.getTime();
HttpServletRequest httpServletRequest=(HttpServletRequest)servletRequest;
HttpServletResponse httpServletResponse=(HttpServletResponse)servletResponse;
HttpSession httpsession=httpServletRequest.getSession();
Object jspzi= httpsession.getAttribute("a");
System.out.println(jspzi);


}

public void destroy() {
}
}