@Override
  DatanodeInfo[] getPipeline() {
    if (this.hdfs_out != null) {
      if (this.hdfs_out.getWrappedStream() instanceof DFSOutputStream) {
        return ((DFSOutputStream) this.hdfs_out.getWrappedStream()).getPipeline();
      }
    }
    return new DatanodeInfo[0];
  }
This method gets the pipeline for the current WAL.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/FSHLog.java