.collect(Collectors.groupingBy(Pair::getFirst, Collectors.mapping(Pair::getSecond, Collectors.toList())));
                    appendJson("search-field", searchFieldMap, buf).append(',');
                    final Map<String, List<String>> requestHeaderMap = entity.getRequestHeaderList()
                            .stream()

   * corresponding to each key appear in the same order as they are encountered.
   *
   * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.groupingBy(keyFunction))}
   * behaves similarly, but returns a mutable {@code Map<K, List<E>>} instead, and may not preserve
   * the order of entries.
   *
   * @param keyFunction the function used to produce the key for each value

   * corresponding to each key appear in the same order as they are encountered.
   *
   * <p><b>{@code Stream} equivalent:</b> {@code stream.collect(Collectors.groupingBy(keyFunction))}
   * behaves similarly, but returns a mutable {@code Map<K, List<E>>} instead, and may not preserve
   * the order of entries.
   *
   * @param keyFunction the function used to produce the key for each value