apollo-portal/src/main/java/com/ctrip/framework/apollo/openapi/server/service/ServerItemOpenApiService.java/ServerItemOpenApiService/getItem
class ServerItemOpenApiService:  @Override
  public OpenItemDTO getItem(String appId, String env, String clusterName, String namespaceName,
      String key) {
    ItemDTO itemDTO = itemService.loadItem(Env.valueOf(env), appId, clusterName, namespaceName, key);
    return itemDTO == null ? null : OpenApiBeanUtils.transformFromItemDTO(itemDTO);
  }