GPhoto2 Java Take Photo

Question

I used this lib github:gphoto2-jna to access my Nikon. I got the preview working (live preview and save the preview image to disk) but I got stuck in capturing a normal photo and save it to the disk. I think my problem is just a pointer thing, but since I'm not working with this stuff its hard for me to figure out this problem :D

This is the code I made:

public void takePhoto() {
 CameraFilePath captureImage = captureImage(_camera, _context);
 PointerByReference pbRef = new PointerByReference(captureImage.getPointer());
 byte[] cameraFileData = getCameraFileData(pbRef, _camera, _context); //from demo
 BufferedImage image = ImageIO.read(new ByteArrayInputStream(cameraFileData));
 //write image to disk
}

public static PointerByReference captureImage(Camera camera, PointerByReference context) {
 CameraFilePath.ByReference cameraPath = new CameraFilePath.ByReference();
 PointerByReference pbRef = new PointerByReference(cameraPath.getPointer());
 {
   check(Gphoto2Library.INSTANCE.gp_file_new(pbRef));
   pbRef.setPointer(pbRef.getValue());
 }
 synchronized (LOCK_OBJECT_CAPTURE) {
   check(Gphoto2Library.INSTANCE.gp_camera_capture(camera, 0, cameraPath, context));
 }
 return cameraPath;
}

public static byte[] getCameraFileData(PointerByReference cameraFile, Camera camera, PointerByReference context) {
 PointerByReference pref = new PointerByReference();
 LongByReference longByRef = new LongByReference();
 int captureRes = check(Gphoto2Library.INSTANCE.gp_file_get_data_and_size(cameraFile, pref, longByRef));
    if (captureRes >= 0) {
        // throws NullPointer
        return pref.getValue().getByteArray(0, (int) longByRef.getValue());
    } else {
        return null;
    }
}

Please let me know if you have any idea how to fix this problem. Thanks in advance!