Https url is not working but http url is working fine in android

Please guide me to find the problem in this code, when i use url with HTTP then it works fine but with HTTPS it's giving problem.I have googled but couldn't find a solution. It would be appreciable if someone guide me to save my time Thanks

public String doRequest() {

    String serverUrl = Constants.BASE_URL + mAction;
    Log.d("usm_serverUrl",serverUrl);
    if (mParams != null) {
        serverUrl += "?" + mParams;
    }
    Log.d("usm_serverUrl",serverUrl);
    try {
        URL url = new URL(serverUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestProperty("User-Agent", "application/json");
       // conn.setRequestMethod("GET");
        if(conn.getResponseCode() == HttpsURLConnection.HTTP_OK){
            // Do normal input or output stream reading
            Log.d("usm_requestCode","Successful");
        }
        else {
            Log.d("usm_requestCode","Failed");
           // response = "FAILED"; // See documentation for more info on response handling
        }
        //HttpURLConnection conn = (HttpURLConnection) url.openConnection();


        InputStream in = new BufferedInputStream(conn.getInputStream());
        Log.d("debug", "get-url: " + serverUrl);
        String response = IOUtils.toString(in, "UTF-8");
        Log.d("debug", "get-url: " + serverUrl + "\n post-response: " + response);
        return response;
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}