JAVA OpenCV：如何将Mat转换为byte？

Question

@RequestMapping(value = "/uploadfiles", method = RequestMethod.POST)
public @ResponseBody
String getFile(MultipartHttpServletRequest request, HttpServletResponse response) {
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    CascadeClassifier faceDetector = new CascadeClassifier("haarcascade_frontalface_alt.xml");

    String imageString = null;

    Iterator<String> itr = request.getFileNames();
    MultipartFile mpf = request.getFile(itr.next());

    try {            
        String fileType = mpf.getContentType(); //image/jpeg

        byte[] basArr = mpf.getBytes();
        InputStream fileIS = mpf.getInputStream();

        Mat basImage = * how convert byte[](basArr) to Mat (basImage)? *;


         //face detection
         MatOfRect faceDetections = new MatOfRect();
         faceDetector.detectMultiScale(basImage, faceDetections);

         for (Rect rect : faceDetections.toArray()) {
            Imgproc.rectangle(basImage, new Point(rect.x, rect.y), new Point(rect.x + rect.width, rect.y + rect.height), new Scalar(0, 255, 0));
         }             

        byte[] resultArr = * how back convert Mat(basImage) to byte[](resultArr) ? *;
        BASE64Encoder encoder = new BASE64Encoder();
        imageString = encoder.encode(resultArr);
    } catch (IOException e) {
        e.printStackTrace();
    }
    return imageString;
}