Utility class which allows you to synchronously get GCM token on Android.

GcmUtil.java

public class GcmUtil {

    public static String getToken(Context context) throws IOException {
        InstanceID instanceID = InstanceID.getInstance(context);
        return instanceID.getToken(context.getString(R.string.gcm_defaultSenderId),
                GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);
    }

    public static String getTokenOnThread(final Context context) {
        try {
            return new AsyncTask<Void, Void, String>() {
                @Override
                protected String doInBackground(Void... params) {
                    try {
                        return getToken(context);
                    } catch (IOException e) {
                        e.printStackTrace();
                        return null;
                    }
                }
            }.execute().get(30L, TimeUnit.SECONDS);
        } catch (InterruptedException | TimeoutException | ExecutionException e) {
            e.printStackTrace();
            return null;
        }
    }
}