HttpURLConnection.getResponseCode throws FileNotFoundException if the
HTTP response code is >=400.

When calling HttpURLConnection.getResponseCode to obtain the HTTP
response code, this method apparently invokes
HttpURLConnection.getInputStream. However, getInputStream will throw
an FileNotFoundException if the HTTP response code is >=400 and the
URL does not end with either ".html", ".htm", "/" or ".txt".

This problem prohibits us from using HttpURLConnection to connect to
non-HTML based URL.