code: private Map<String, List<CmsContainerBean>> getContainerByParent(CmsContainerPageBean page) {
  
          Map<String, List<CmsContainerBean>> containerByParent = new HashMap<String, List<CmsContainerBean>>();
  
          for (CmsContainerBean container : page.getContainers().values()) {
              if (container.getParentInstanceId() != null) {
                  if (!containerByParent.containsKey(container.getParentInstanceId())) {
                      containerByParent.put(container.getParentInstanceId(), new ArrayList<CmsContainerBean>());
                  }
                  containerByParent.get(container.getParentInstanceId()).add(container);
              }
          }
          return containerByParent;
      }
docs: Collects the page containers by parent instance id.<p>
  
  @param page the page
  
  @return the containers by parent id