code: public void consumeKeyMessage(String key, U message, Configuration hadoopConf) throws IOException {
      log.info("{} : {}", key, message);
    }
docs: Convenience method that is called by the default implementation of
  {@link #consume(Iterator, Configuration)}, to process one key-message pair.
  It does nothing, except log the message. This should generally be overridden
  if and only if {@link #consume(Iterator, Configuration)} is not.
  
  @param key key to process (non-null)
  @param message message to process
  @param hadoopConf Hadoop configuration for process
  @throws IOException if an error occurs while processing the message
  @since 2.3.0