code: private void replaceHostLabelsWithStringSpecifier(String hostExpression) {
          if (StringUtils.isNullOrEmpty(hostExpression)) {
              throw new IllegalArgumentException("Given host prefix is either null or empty");
          }
  
          Matcher matcher = PATTERN.matcher(hostExpression);
  
          while (matcher.find()) {
              String matched = matcher.group(1);
              c2jNames.add(matched);
              hostWithStringSpecifier = hostWithStringSpecifier.replaceFirst("\\{" + matched + "}", "%s");
          }
      }
docs: Replace all the labels in host with %s symbols and collect the input shape member names into a list