apollo-adminservice/src/main/java/com/ctrip/framework/apollo/adminservice/controller/ItemController.java/ItemController/get
class ItemController:  @GetMapping("/apps/{appId}/clusters/{clusterName}/namespaces/{namespaceName}/items/{key:.+}")
  public ItemDTO get(@PathVariable("appId") String appId,
      @PathVariable("clusterName") String clusterName,
      @PathVariable("namespaceName") String namespaceName, @PathVariable("key") String key) {
    Item item = itemService.findOne(appId, clusterName, namespaceName, key);
    if (item == null) {
      throw new NotFoundException("item not found for %s %s %s %s", appId, clusterName,
          namespaceName, key);
    }
    return BeanUtils.transform(ItemDTO.class, item);
  }