getting java.net.UnknownHostException while sending request to https://www.googleapis.com/

Question

I have the following code which uses google URL shortening service. The code runs just fine but when run with the proxy it returns a unknown host exception Is there a way to hit http://www.googleapis.com with authentication through my code .

I have used the following code:

String json = "{\"longUrl\": \""+longUrl+"\"}";   
String apiURL = GOOGLE_URL_SHORT_API+"?key="+GOOGLE_API_KEY;


System.setProperty("proxySet", "true");
System.setProperty("http.proxyHost", proxyHost);
System.setProperty("http.proxyPort", proxyPort);    

AuthCacheValue.setAuthCache(new AuthCacheImpl());
Authenticator.setDefault(new Authenticator() 
{
    protected PasswordAuthentication getPasswordAuthentication() 
    {
    return new PasswordAuthentication(proxyUser,proxyPassword.toCharArray());
    }
});


HttpPost postRequest = new HttpPost(apiURL);
postRequest.setHeader("Content-Type", "application/json");
postRequest.setEntity(new StringEntity(json, "UTF-8"));

CloseableHttpClient httpClient = HttpClients.createDefault();
HttpResponse response = httpClient.execute(postRequest);
String responseText = EntityUtils.toString(response.getEntity());           

Gson gson = new Gson();
@SuppressWarnings("unchecked")
HashMap<String, String> res = gson.fromJson(responseText, HashMap.class);

Need suggestions.