apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/api/AdminServiceAPI.java/AdminServiceAPI/loadItem
class AdminServiceAPI:    public ItemDTO loadItem(Env env, String appId, String clusterName, String namespaceName, String key) {
      return restTemplate.get(env, "apps/{appId}/clusters/{clusterName}/namespaces/{namespaceName}/items/{key}",
          ItemDTO.class, appId, clusterName, namespaceName, key);
    }