apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/service/PortalDBPropertySource.java/PortalDBPropertySource/refresh
class PortalDBPropertySource:  @Override
  protected void refresh() {
    Iterable<ServerConfig> dbConfigs = serverConfigRepository.findAll();

    for (ServerConfig config: dbConfigs) {
      String key = config.getKey();
      Object value = config.getValue();

      if (this.source.isEmpty()) {
        logger.info("Load config from DB : {} = {}", key, value);
      } else if (!Objects.equals(this.source.get(key), value)) {
        logger.info("Load config from DB : {} = {}. Old value = {}", key,
                    value, this.source.get(key));
      }

      this.source.put(key, value);
    }
  }