code: public static void setOutputFormat(Class<?> realOutputFormatClass, JobConf jobConf) {
      jobConf.setOutputFormat(DeprecatedOutputFormatWrapper.class);
      HadoopUtils.setClassConf(jobConf, CLASS_CONF_KEY, realOutputFormatClass);
    }
docs: Sets jobs output format to {@link DeprecatedOutputFormatWrapper} and stores
  supplied real {@link OutputFormat} class name in job configuration.
  This configuration is read on the remote tasks to instantiate actual
  OutputFormat correctly.