apollo-core/src/main/java/com/ctrip/framework/apollo/core/MetaDomainConsts.java/MetaDomainConsts/schedulePeriodicRefresh
class MetaDomainConsts:  private static void schedulePeriodicRefresh() {
    ScheduledExecutorService scheduledExecutorService =
        Executors.newScheduledThreadPool(1, ApolloThreadFactory.create("MetaServiceLocator", true));

    scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
      @Override
      public void run() {
        try {
          for (String metaServerAddresses : selectedMetaServerAddressCache.keySet()) {
            updateMetaServerAddresses(metaServerAddresses);
          }
        } catch (Throwable ex) {
          logger
              .warn(String.format("Refreshing meta server address failed, will retry in %d seconds",
                  REFRESH_INTERVAL_IN_SECOND), ex);
        }
      }
    }, REFRESH_INTERVAL_IN_SECOND, REFRESH_INTERVAL_IN_SECOND, TimeUnit.SECONDS);
  }