rateService.inc("event-name");

rateService.get("event-name");

HashMap<String>, List<AtomicLong>>

HashMap<String>, List<AtomicLong>>

package status;


import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class RateCounterService {

    private final int capacity;
    private Map<String, List<AtomicInteger>> stats = new ConcurrentHashMap<>();
    private volatile long currentTimestamp = Instant.now().getEpochSecond();
    private final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();

    public RateCounterService(int capacity) {
        this.capacity = capacity;
        executorService.scheduleAtFixedRate(() -> {
            currentTimestamp = Instant.now().getEpochSecond();
            int index = getIndex(0);
            for (Map.Entry<String, List<AtomicInteger>> entry : stats.entrySet()) {
                stats.get(entry.getKey()).get(index).set(0);
            }
        }, 1, 1, TimeUnit.SECONDS);
    }

    public void inc(String statName) {
        int index = getIndex(0);
        stats.computeIfAbsent(statName, k -> {
            List<AtomicInteger> list = new ArrayList<>(capacity);
            for (int i = 0; i < capacity; i++) {
                list.add(i, new AtomicInteger(0));
            }
            return list;
        });
        stats.get(statName).get(index).incrementAndGet();
    }

    /**
     * @param statName any string key
     * @return amount of events, measured in the previous time unit (the current is still filling)
     */
    public Integer get(String statName) {
        int index = getIndex(-1);
        return stats.get(statName).get(index).get();
    }

    public long getTotal(String statName, int units) throws RateCounterException {
        long total = 0L;
        if (units < 0) {
            throw new RateCounterException("units can be greater than 0");
        }
        if (units > capacity) {
            throw new RateCounterException("units can not be greater than `capacity`");
        }
        List<AtomicInteger> list = stats.get(statName);
        for (int i = units; i > 0; i--) {
            int index = getIndex(-i - 1);
            total += list.get(index).get();
        }
        return total;
    }

    private int getIndex(int correction) {
        return (int) ((currentTimestamp + correction) % capacity);
    }

}