core/src/main/java/com/twitter/elephantbird/mapreduce/input/MultiInputFormat.java
public static void setClassConf(Class<?> clazz, Configuration conf) {
    HadoopUtils.setClassConf(conf, CLASS_CONF_KEY, clazz);
  }
public static void setClassConf(Class<?> clazz, Configuration conf) {
    HadoopUtils.setClassConf(conf, CLASS_CONF_KEY, clazz);
  }
Stores supplied class name in configuration. This configuration is
read on the remote tasks to initialize the input format correctly.