@Override
  public void onConfigurationChange(Configuration conf) {
    cacheDataOnRead = conf.getBoolean(CACHE_DATA_ON_READ_KEY, DEFAULT_CACHE_DATA_ON_READ);
    cacheDataOnWrite = conf.getBoolean(CACHE_BLOCKS_ON_WRITE_KEY, DEFAULT_CACHE_DATA_ON_WRITE);
    evictOnClose = conf.getBoolean(EVICT_BLOCKS_ON_CLOSE_KEY, DEFAULT_EVICT_ON_CLOSE);
    LOG.info(
      "Config hbase.block.data.cacheonread is changed to {}, "
        + "hbase.rs.cacheblocksonwrite is changed to {}, "
        + "hbase.rs.evictblocksonclose is changed to {}",
      cacheDataOnRead, cacheDataOnWrite, evictOnClose);
  }
Returns the block cache.
@return the block cache, or null if caching is completely disabled
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/CacheConfig.java