public static List<String> getSortedListByKeys(HashMap<String,String> keysDictionary)
    {
        List<String> sortedKeysList = null;
        SortedSet<String> sortedKeysSet = null;

        if(keysDictionary == null || keysDictionary.size() == 0){
            return null;
        }

        sortedKeysSet = new TreeSet<>(keysDictionary.keySet());
        sortedKeysList = new ArrayList<>(sortedKeysSet);

        return sortedKeysList;
    }

sortedKeysList = new ArrayList<>(keysDictionary.keySet());
Collections.sort(sortedKeysList);

Map<String, String> keysDictionary = new HashMap<>();
List<String> sortedKeys = keysDictionary.keySet().stream()
        .sorted()
        .collect(Collectors.toList());