code: public SimpleJob setSimpleJoin(String[] masterLabels, String[] masterColumns, String[] dataColumns,
              String masterPath, String separator, boolean regex) throws DataFormatException {
          if (masterColumns.length != dataColumns.length) {
              throw new DataFormatException("masterColumns and dataColumns lenght is miss match.");
          }
  
          conf.setInt(READER_TYPE, SOME_COLUMN_JOIN_READER);
          conf.setStrings(MASTER_LABELS, masterLabels);
          conf.setStrings(JOIN_MASTER_COLUMN, masterColumns);
          conf.setStrings(JOIN_DATA_COLUMN, dataColumns);
          conf.set(MASTER_PATH, masterPath);
          conf.set(MASTER_SEPARATOR, separator);
          conf.setBoolean(JOIN_REGEX, regex);
          return this;
      }
docs: Easily supports the Join. To use the setSimpleJoin,
  you must be a size master data appear in the memory of the task.
  @param masterLabels label of master data
  @param masterColumns master column's
  @param dataColumns data column's
  @param masterPath master data HDFS path
  @param separator separator
  @param regex master join is regex
  @return this
  @throws DataFormatException