code: public static String regexpExtract(String str, String regex, int extractIndex) {
  		if (extractIndex < 0) {
  			return null;
  		}
  
  		try {
  			Matcher m = REGEXP_PATTERN_CACHE.get(regex).matcher(str);
  			if (m.find()) {
  				MatchResult mr = m.toMatchResult();
  				return mr.group(extractIndex);
  			}
  			return null;
  		} catch (Exception e) {
  			LOG.error(
  				String.format("Exception in regexpExtract('%s', '%s', '%d')", str, regex, extractIndex),
  				e);
  			return null;
  		}
  	}
docs: Returns a string extracted with a specified regular expression and a regex
  match group index.