apollo-core/src/main/java/com/ctrip/framework/apollo/core/utils/NetUtil.java/NetUtil/pingUrl
class NetUtil:  public static boolean pingUrl(String address) {
    try {
      URL urlObj = new URL(address);
      HttpURLConnection connection = (HttpURLConnection) urlObj.openConnection();
      connection.setRequestMethod("GET");
      connection.setUseCaches(false);
      connection.setConnectTimeout(DEFAULT_TIMEOUT_IN_SECONDS);
      connection.setReadTimeout(DEFAULT_TIMEOUT_IN_SECONDS);
      int statusCode = connection.getResponseCode();
      cleanUpConnection(connection);
      return (200 <= statusCode && statusCode <= 399);
    } catch (Throwable ignore) {
    }
    return false;
  }