Apollo client change listener

ApolloClientChangeListenerDemo.java

Config config = ConfigService.getAppConfig();
config.addChangeListener(new ConfigChangeListener() {
  @Override
  public void onChange(ConfigChangeEvent changeEvent) {
    for (String key : changeEvent.changedKeys()) {
      ConfigChange change = changeEvent.getChange(key);
      System.out.println(String.format(
        "Found change - key: %s, oldValue: %s, newValue: %s, changeType: %s",
        change.getPropertyName(), change.getOldValue(),
        change.getNewValue(), change.getChangeType()));
     }
  }
});