apollo-client/src/main/java/com/ctrip/framework/apollo/util/ConfigUtil.java/ConfigUtil/getDefaultLocalCacheDir
class ConfigUtil:  public String getDefaultLocalCacheDir() {
    String cacheRoot = getCustomizedCacheRoot();

    if (!Strings.isNullOrEmpty(cacheRoot)) {
      return cacheRoot + File.separator + getAppId();
    }

    cacheRoot = isOSWindows() ? "C:\\opt\\data\\%s" : "/opt/data/%s";
    return String.format(cacheRoot, getAppId());
  }