public Map<String, Set<NearFinderData>> getDataMap() {
        Map<String, Set<NearFinderData>> latestData = null;
        lock.readLock().lock();
        try {
            latestData = NEAR_FINDER_DATA;
        } finally {
            lock.readLock().unlock();
        }
        return latestData;
    }

和

public Map<String, Set<NearFinderData>> getDataMap() {
        lock.readLock().lock();
        try {
            return NEAR_FINDER_DATA;
        } finally {
            lock.readLock().unlock();
        }

    }

的区别是什么呢？其中NEAR_FINDER_DATA 是一个被修改的Map