@Override public String toString() {
    return "KafkaSupervisorSpec{"
        + "dataSchema="
        + dataSchema
        + ", tuningConfig="
        + tuningConfig
        + ", ioConfig="
        + ioConfig
        + '}';
  }
This class is copied from druid source code
in order to avoid adding additional dependencies on druid-indexing-service.
druid-handler/src/java/org/apache/hadoop/hive/druid/json/KafkaSupervisorSpec.java