default Cacheable getBlock(BlockCacheKey cacheKey, boolean caching, boolean repeat,
    boolean updateCacheMetrics, BlockType blockType) {
    return getBlock(cacheKey, caching, repeat, updateCacheMetrics);
  }
Fetch block from cache.
@param cacheKey           Block to fetch.
@param caching            Whether this request has caching enabled (used for stats)
@param repeat             Whether this is a repeat lookup for the same block (used to avoid
                          double counting cache misses when doing double-check locking)
@param updateCacheMetrics Whether to update cache metrics or not
@param blockType          BlockType
@return Block or null if block is not in 2 cache.
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/BlockCache.java