presto-hive/src/main/java/io/prestosql/plugin/hive/BackgroundHiveSplitLoader.java/BackgroundHiveSplitLoader/createInternalHiveSplitIterator
class BackgroundHiveSplitLoader:    private Iterator<InternalHiveSplit> createInternalHiveSplitIterator(Path path, FileSystem fileSystem, InternalHiveSplitFactory splitFactory, boolean splittable)
    {
        return Streams.stream(new HiveFileIterator(table, path, fileSystem, directoryLister, namenodeStats, recursiveDirWalkerEnabled ? RECURSE : IGNORED))
                .map(status -> splitFactory.createInternalHiveSplit(status, splittable))
                .filter(Optional::isPresent)
                .map(Optional::get)
                .iterator();
    }