Post over https using HttpUrlConnection

Having problems getting a POST over https to work through a proxy. A
GET over http through the proxy works fine. A Post over https works
fine when not behind a proxy, but when behind a proxy then it does not
work:
javax.net.ssl.SSLHandshakeException: Remote host closed connection
during handshake.

Any help is appreciated.
Axel

Here a code snippet for the GET that works fine:

    String site = "http://www.example.com";
    try {
            // with Proxy
            URL url = new URL(
                    "http", // protocol
                    "proxyhostname", // host name or IP of proxy server
                    80, // proxy port
                    site); // URL

            String userPassword = "domain\\user" + ":" + "password";
    String encodedUserPassword = new BASE64Encoder()
    .encode(userPassword.getBytes());

    HttpURLConnection con = (HttpURLConnection) url.openConnection();
    con.setRequestProperty("Proxy-Authorization", "Basic "
    + encodedUserPassword);

            InputStream in = con.getInputStream();
            InputStreamReader inReader = new InputStreamReader(in);
            BufferedReader bufReader = new BufferedReader(inReader);

            String inputLine;
            while ((inputLine = bufReader.readLine()) != null)
               System.out.println(inputLine);

            in.close();

        } catch (Exception e) {
            // exception handling
        }

Here a code snippet that does not function:

        String site = "https://www.example.com/dosomething";
        try {

            // with Proxy
            URL url = new URL(
                "https", // protocol
                "proxyhostname", // host name or IP of proxy server
                443, // proxy port
                site); // URL
            String userPassword = "domain\\user" + ":" + "password";
            String encodedUserPassword = new BASE64Encoder()
                .encode(userPassword.getBytes());

            HttpURLConnection con = (HttpURLConnection) url.openConnection();
            con.setRequestProperty("Proxy-Authorization", "Basic "
                + encodedUserPassword);

            String parametersAsString;
            byte[] parametersAsBytes;

            parametersAsString = "param1=value1" +
                                 "&param2=value2";
            parametersAsBytes = parametersAsString.getBytes();

            con.setRequestMethod("POST");
            con.setRequestProperty("Content-Length", "" +
                    Integer.toString(parametersAsBytes.length));

            con.setUseCaches(false);
            con.setDoInput(true);
            con.setDoOutput(true);

            OutputStream dataOut = con.getOutputStream();
            dataOut.write(parametersAsBytes);
            dataOut.flush();
            dataOut.close();

            InputStream in = con.getInputStream();
            InputStreamReader inReader = new InputStreamReader(in);
            BufferedReader bufReader = new BufferedReader(inReader);

            String inputLine;
            while ((inputLine = bufReader.readLine()) != null)
                System.out.println(inputLine);

            in.close();

        } catch (Exception e) {
            // exception handling
        }