Extract Regexp named group candidates

RegexUtils.java

public static Set<String> getNamedGroupCandidates(String regex) {
    Set<String> namedGroups = new TreeSet<>();
    Matcher m = Pattern.compile("\\(\\?<([a-zA-Z0-9]*)>").matcher(regex);
    while (m.find()) {
        namedGroups.add(m.group(1));
    }
    return namedGroups;
}