apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/controller/InstanceController.java/InstanceController/getByNamespace
class InstanceController:    @GetMapping("/envs/{env}/instances/by-namespace")
    public PageDTO<InstanceDTO> getByNamespace(@PathVariable String env, @RequestParam String appId,
                                               @RequestParam String clusterName, @RequestParam String namespaceName,
                                               @RequestParam(required = false) String instanceAppId,
                                               @RequestParam(defaultValue = "0") int page,
                                               @RequestParam(defaultValue = "20") int size) {

        return instanceService.getByNamespace(Env.valueOf(env), appId, clusterName, namespaceName, instanceAppId, page, size);
    }