QrGenerator.java

private byte[] generateQrImage(String content) throws WriterException, IOException {
        // Create new configuration that specifies the error correction
        Map<EncodeHintType, ErrorCorrectionLevel> hints = new HashMap<>();
        hints.put(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.M);

        // Create a qr code with the url as content and a size of WxH px
        BitMatrix bitMatrix = new QRCodeWriter().encode(content, BarcodeFormat.QR_CODE, WIDTH, HEIGHT, hints);

        // Load QR image
        BufferedImage qrImage = MatrixToImageWriter.toBufferedImage(bitMatrix, new MatrixToImageConfig(BLACK, WHITE));

        // Load logo image
        BufferedImage overly = getOverly(LOGO);

        // Calculate the delta height and width between QR code and logo
        int deltaHeight = qrImage.getHeight() - overly.getHeight();
        int deltaWidth = qrImage.getWidth() - overly.getWidth();

        // Initialize combined image
        BufferedImage combined = new BufferedImage(qrImage.getHeight(), qrImage.getWidth(), BufferedImage.TYPE_INT_ARGB);
        Graphics2D g = (Graphics2D) combined.getGraphics();

        // Write QR code to new image at position 0/0
        g.drawImage(qrImage, 0, 0, null);
        g.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 1f));

        // Write logo into combine image at position (deltaWidth / 2) and
        // (deltaHeight / 2). Background: Left/Right and Top/Bottom must be
        // the same space for the logo to be centered
        g.drawImage(overly, deltaWidth/2, deltaHeight/2, null);
        g.dispose();
        
        // Write combined image as PNG to OutputStream
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(combined, "png", os);
        os.toByteArray();
        os.close();

        return os.toByteArray();
    }