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