public class GetMsgServlet extends HttpServlet {
    /**
     * 用于存放请求IP以及时间戳数据
     */
    private static final Map<String, Long> REQ_IP_CACHE = 
        new HashMap<String, Long>();
    /**
     * 限定的请求时间间隔, 5s
     */
    private final static long TimeInterval = 5000;
    // 你的其他代码
    public void doGet(HttpServletRequest req, HttpServletResponse resp) {
        // 你预先要处理的一些代码.
        boolean isFast = false;
        String reqIp = req.getRemoteAddr();
        Long timestamp = Long.valueOf(System.currentTimeMillis());
        if ( REQ_IP_CACHE.contains(reqIp) ) {
            Long storedTime = REQ_IP_CACHE.get(reqIp);
            if ( (storedTime+TimeInterval) > timestamp ) {
                isFast = true;
            } else {
                REQ_IP_CACHE.put(reqIp, timestamp);
            }
        } else {
            REQ_IP_CACHE.put(reqIp, timestamp);
        }
        if ( !isFast ) {
            // 你的业务代码        
        }
    }
}