code: public static String splitIndex(String str, String separator, int index) {
  		if (index < 0) {
  			return null;
  		}
  		String[] values = StringUtils.splitByWholeSeparatorPreserveAllTokens(str, separator);
  		if (index >= values.length) {
  			return null;
  		} else {
  			return values[index];
  		}
  	}
docs: Split target string with custom separator and pick the index-th(start with 0) result.
  
  @param str       target string.
  @param separator custom separator.
  @param index     index of the result which you want.
  @return the string at the index of split results.