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

        scheduledExecutorService.scheduleAtFixedRate(() -> {
            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);
    }