Rate Limiter

Whenever you expose a web service / api endpoint, you need to implement a rate limiter to prevent abuse of the service (DOS attacks).

Implement a RateLimiter Class with an isAllow method. Every request comes in with a unique clientID, deny a request if that client has made more than 100 requests in the past second.

 public class RateLimiter {
     private final Map<String, LinkedList<Long>> clientHitMap = new HashMap<>();
     private final int REQUEST_LIMIT = ;
     private final long TIME_LIMIT = 1000L;

     public boolean isAllow(String client_id) {
         LinkedList<Long> list = clientHitMap.get(client_id);
         long curTime = System.currentTimeMillis();
         if (list == null) {
             clientHitMap.put(client_id, new LinkedList<Long>());
         }
         while (!list.isEmpty() && curTime - list.peek() >= TIME_LIMIT) {
             list.poll();
         }
         if (list.size() < REQUEST_LIMIT) {
             list.offer(curTime);
             return true;
         }
         return false;
     }
 }