Rate Limiter in Java

RateLimiter.java

import java.time.Duration;

public class RateLimiter {

    private long capacity;
    private long lastRefillTimeStamp;
    private long refillCountPerSecond;
    private long availableTokens;

    public RateLimiter(long capacity, Duration window) {
        this.capacity = capacity;
        lastRefillTimeStamp = System.currentTimeMillis();
        refillCountPerSecond = capacity / window.getSeconds();
        availableTokens = 0;
    }

    public long getAvailableTokens() {
        return this.availableTokens;
    }

    public synchronized boolean tryConsume() {
        refill();

        if (availableTokens > 0) {
            --availableTokens;
            return true;
        } else {
            return false;
        }
    }

    private void refill() {
        long now = System.currentTimeMillis();
        if (now > lastRefillTimeStamp) {
            long elapsedTime = now - lastRefillTimeStamp;
            long tokensToBeAdded = (elapsedTime / 1000) * refillCountPerSecond;
            if (tokensToBeAdded > 0) {
                availableTokens = Math.min(capacity, availableTokens + tokensToBeAdded);
                lastRefillTimeStamp = now;

            }
        }
    }
}

RateLimitFactory.java

import java.time.Duration;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

public class RateLimitFactory {

    private final ConcurrentMap<String, RateLimiter> rateLimiters = new ConcurrentHashMap<>();
    private long capacity;
    private Duration window;

    public RateLimitFactory(long capacity, Duration window) {
        this.capacity = capacity;
        this.window = window;
    }

    public RateLimiter get(String key) {
        return rateLimiters.computeIfAbsent(key, k -> new RateLimiter(capacity, window));
    }
}