code: public SimpleJob setSimpleJoin(String[] masterLabels, String masterColumn, String dataColumn,
                                     String masterPath, String separator, boolean regex) {
          conf.setInt(READER_TYPE, SINGLE_COLUMN_JOIN_READER);
          conf.setStrings(MASTER_LABELS, masterLabels);
          conf.set(JOIN_MASTER_COLUMN, masterColumn);
          conf.set(JOIN_DATA_COLUMN, dataColumn);
          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 masterColumn master column
  @param dataColumn data column
  @param masterPath master data HDFS path
  @param separator separator
  @param regex master join is regex
  @return this