core/src/main/java/com/twitter/elephantbird/util/HadoopUtils.java
public static void writeStringListToConfAsJson(String key,
                                                 List<String> list,
                                                 Configuration conf) {
    Preconditions.checkNotNull(list);
    conf.set(key, JSONArray.toJSONString(list));
  }
public static void writeStringListToConfAsJson(String key,
                                                 List<String> list,
                                                 Configuration conf) {
    Preconditions.checkNotNull(list);
    conf.set(key, JSONArray.toJSONString(list));
  }
Writes a list of strings into a configuration by converting it to a json array

@param key for the configuration
@param list to write
@param conf to write to