apollo-client/src/main/java/com/ctrip/framework/apollo/spring/config/NamespaceHandler.java/BeanParser/doParse
class BeanParser:    @Override
    protected void doParse(Element element, BeanDefinitionBuilder builder) {
      String namespaces = this.resolveNamespaces(element);

      int order = Ordered.LOWEST_PRECEDENCE;
      String orderAttribute = element.getAttribute("order");

      if (!Strings.isNullOrEmpty(orderAttribute)) {
        try {
          order = Integer.parseInt(orderAttribute);
        } catch (Throwable ex) {
          throw new IllegalArgumentException(
              String.format("Invalid order: %s for namespaces: %s", orderAttribute, namespaces));
        }
      }
      PropertySourcesProcessor.addNamespaces(NAMESPACE_SPLITTER.splitToList(namespaces), order);
    }