apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/controller/ConfigController.java/ConfigController/findPublicConfig
class ConfigController:  private Release findPublicConfig(String clientAppId, String clientIp, String clientLabel, String clusterName,
                                   String namespace, String dataCenter, ApolloNotificationMessages clientMessages) {
    AppNamespace appNamespace = appNamespaceService.findPublicNamespaceByName(namespace);

    //check whether the namespace's appId equals to current one
    if (Objects.isNull(appNamespace) || Objects.equals(clientAppId, appNamespace.getAppId())) {
      return null;
    }

    String publicConfigAppId = appNamespace.getAppId();

    return configService.loadConfig(clientAppId, clientIp, clientLabel, publicConfigAppId, clusterName, namespace, dataCenter,
        clientMessages);
  }