@Override
  public Optional<Boolean> shouldCacheFile(String fileName) {
    Optional<Boolean> l1Result = l1Cache.shouldCacheFile(fileName);
    Optional<Boolean> l2Result = l2Cache.shouldCacheFile(fileName);
    final Mutable<Boolean> combinedResult = new MutableBoolean(true);
    l1Result.ifPresent(b -> combinedResult.setValue(b && combinedResult.getValue()));
    l2Result.ifPresent(b -> combinedResult.setValue(b && combinedResult.getValue()));
    return Optional.of(combinedResult.getValue());
  }
Returns the list of fully cached files
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/CombinedBlockCache.java