redis-bitmaps-2.java

import redis.clients.jedis.Jedis;
import java.util.BitSet;

Jedis redis = new Jedis("localhost");

public int uniqueCount(String action, String... dates) {
    BitSet all = new BitSet();
    for (String date : dates) {
        String key = action + ":" + date;
        BitSet users = BitSet.valueOf(redis.get(key.getBytes()));
        all.or(users);
    }
    return all.cardinality();
}