public static WALStreamReader createStreamReader(FileSystem fs, Path path, Configuration conf,
    long startPosition) throws IOException {
    return getInstance(conf).createStreamReader(fs, path, (CancelableProgressable) null,
      startPosition);
  }
Create a one-way stream reader for a given path.
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALFactory.java