public ConsumerFilterData get(final String topic, final String consumerGroup) {
        if (!this.filterDataByTopic.containsKey(topic)) {
            return null;
        }
        if (this.filterDataByTopic.get(topic).getGroupFilterData().isEmpty()) {
            return null;
        }

        return this.filterDataByTopic.get(topic).getGroupFilterData().get(consumerGroup);
    }
@Test
    public void testPersist_clean() {
        ConsumerFilterManager filterManager = gen(10, 10);

        String topic = "topic9";
        for (int i = 0; i < 10; i++) {
            String cid = "CID_" + i;

            ConsumerFilterData filterData = filterManager.get(topic, cid);

            assertThat(filterData).isNotNull();
            assertThat(filterData.isDead()).isFalse();

            //make dead more than 24h
            filterData.setBornTime(System.currentTimeMillis() - 26 * 60 * 60 * 1000);
            filterData.setDeadTime(System.currentTimeMillis() - 25 * 60 * 60 * 1000);
        }

        try {
            filterManager.persist();

            ConsumerFilterManager loadFilter = new ConsumerFilterManager();

            assertThat(loadFilter.load()).isTrue();

            ConsumerFilterData filterData = loadFilter.get(topic, "CID_9");

            assertThat(filterData).isNull();

            Collection<ConsumerFilterData> topicData = loadFilter.get(topic);

            assertThat(topicData).isNullOrEmpty();
        } finally {
            UtilAll.deleteFile(new File("./unit_test"));
        }
    }