code: private HttpURLConnection openHttp() throws IOException {
  		final URLConnection conn = openConnection();
  		if (false == conn instanceof HttpURLConnection) {
  			// 防止其它协议造成的转换异常
  			throw new HttpException("'{}' is not a http connection, make sure URL is format for http.", conn.getClass().getName());
  		}
  
  		return (HttpURLConnection) conn;
  	}
docs: 初始化http或https请求参数<br>
  有些时候htts请求会出现com.sun.net.ssl.internal.www.protocol.https.HttpsURLConnectionOldImpl的实现，此为sun内部api，按照普通http请求处理
  
  @param hostnameVerifier 域名验证器，非https传入null
  @param ssf SSLSocketFactory，非https传入null
  @return {@link HttpURLConnection}，https返回{@link HttpsURLConnection}