apollo-demo/src/main/java/com/ctrip/framework/apollo/demo/api/SimpleApolloConfigDemo.java/SimpleApolloConfigDemo/SimpleApolloConfigDemo
class SimpleApolloConfigDemo:  public SimpleApolloConfigDemo() {
    ConfigChangeListener changeListener = new ConfigChangeListener() {
      @Override
      public void onChange(ConfigChangeEvent changeEvent) {
        logger.info("Changes for namespace {}", changeEvent.getNamespace());
        for (String key : changeEvent.changedKeys()) {
          ConfigChange change = changeEvent.getChange(key);
          logger.info("Change - key: {}, oldValue: {}, newValue: {}, changeType: {}",
              change.getPropertyName(), change.getOldValue(), change.getNewValue(),
              change.getChangeType());
        }
      }
    };
    config = ConfigService.getAppConfig();
    config.addChangeListener(changeListener);
  }