@Override
  public void checkOutputSpecs(FileSystem ignored, JobConf job) throws IOException {
    MapredWork work = Utilities.getMapRedWork(job);

    List<Operator<?>> opList = work.getAllOperators();

    for (Operator<?> op : opList) {
      if (op instanceof FileSinkOperator) {
        ((FileSinkOperator) op).checkOutputSpecs(ignored, job);
      }
    }
  }
Hive does not use OutputFormat's in a conventional way, but constructs and uses
the defined OutputFormat for each table from FileSinkOperator. HiveOutputFormatImpl is
used for basic setup, especially for calling checkOutputSpecs().
ql/src/java/org/apache/hadoop/hive/ql/io/HiveOutputFormatImpl.java