apollo-client/src/main/java/com/ctrip/framework/apollo/spring/spi/DefaultApolloConfigRegistrarHelper.java/DefaultApolloConfigRegistrarHelper/logNamespacePlaceholderNotSupportedMessage
class DefaultApolloConfigRegistrarHelper:  private void logNamespacePlaceholderNotSupportedMessage(String[] namespaces) {
    for (String namespace : namespaces) {
      if (namespace.contains("${")) {
        logger.warn("Namespace placeholder {} is not supported for Spring version prior to 3.2.x,"
                + " see https://github.com/apolloconfig/apollo/issues/4178 for more details.",
            namespace);
        break;
      }
    }
  }