code: protected HttpURLConnection openConnection(URL url, Proxy proxy) throws IOException {
  		URLConnection urlConnection = (proxy != null ? url.openConnection(proxy) : url.openConnection());
  		Assert.isInstanceOf(HttpURLConnection.class, urlConnection);
  		return (HttpURLConnection) urlConnection;
  	}
docs: Opens and returns a connection to the given URL.
  <p>The default implementation uses the given {@linkplain #setProxy(java.net.Proxy) proxy} -
  if any - to open a connection.
  @param url the URL to open a connection to
  @param proxy the proxy to use, may be {@code null}
  @return the opened connection
  @throws IOException in case of I/O errors