apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/api/AdminServiceAPI.java/InstanceAPI/getByNamespace
class InstanceAPI:    public PageDTO<InstanceDTO> getByNamespace(String appId, Env env, String clusterName, String namespaceName,
        String instanceAppId,
        int page, int size) {
      ResponseEntity<PageDTO<InstanceDTO>>
          entity =
          restTemplate.get(env,
              "/instances/by-namespace?appId={appId}"
                  + "&clusterName={clusterName}&namespaceName={namespaceName}&instanceAppId={instanceAppId}"
                  + "&page={page}&size={size}",
              pageInstanceDtoType, appId, clusterName, namespaceName, instanceAppId, page, size);
      return entity.getBody();
    }