private List<String> readFileFromHDFS(final String filename) throws IOException {
    final Path path = new Path(filename);
    final FileSystem fs = FileSystem.get(this.conf);
    try (BufferedReader reader =
      new BufferedReader(new InputStreamReader(fs.open(path), StandardCharsets.UTF_8))) {
      return CharStreams.readLines(reader);
    }
  }
used to read the rule files from HDFS
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/HeterogeneousRegionCountCostFunction.java