apollo-portal/src/main/java/com/ctrip/framework/apollo/openapi/v1/controller/ItemController.java/ItemController/getItem
class ItemController:  @GetMapping(value = "/apps/{appId}/clusters/{clusterName}/namespaces/{namespaceName}/items/{key:.+}")
  public OpenItemDTO getItem(@PathVariable String appId, @PathVariable String env, @PathVariable String clusterName,
      @PathVariable String namespaceName, @PathVariable String key) {
    return this.itemOpenApiService.getItem(appId, env, clusterName, namespaceName, key);
  }