public LocalFileConfigRepository(String namespace, ConfigRepository upstream) {
    m_namespace = namespace;
    m_configUtil = ApolloInjector.getInstance(ConfigUtil.class);
    this.setLocalCacheDir(findLocalCacheDir(), false);
    this.setUpstreamRepository(upstream); 
    this.trySync();   
  }

public void setUpstreamRepository(ConfigRepository upstreamConfigRepository) {
    ...
    trySyncFromUpstream();
    upstreamConfigRepository.addChangeListener(this);
  }

protected void sync() {
    //sync with upstream immediately
    boolean syncFromUpstreamResultSuccess = trySyncFromUpstream();
}