public LRUCacheEntry get(final String namespace, final Bytes key) {
        numGets++;

        if (key == null) {
            return null;
        }

        final NamedCache cache = getCache(namespace);
        if (cache == null) {
            return null;
        }
        return cache.get(key);
    }
Add a listener that is called each time an entry is evicted from the cache or an explicit flush is called
streams/src/main/java/org/apache/kafka/streams/state/internals/ThreadCache.java