zxing生成高容错率二维码，以及添加文字

知识点：

1.使用zxing组件生成二维码

2.向二维码图片添加文本内容

3.设置二维码容错率（避免扫码识别率低）

    public String saveQRCode(String id, String name, String content, String fileName, String formatName) {
        String imageUri = null;
        File file = null;
        try {
            StringBuffer buf = new StringBuffer(fileConfig.getStorageDir());
            buf.append(File.separator).append("qrcode").append(fileName);
            imageUri = buf.toString();

            file = new File(imageUri);
            if (!file.getParentFile().exists()) {
                file.getParentFile().mkdirs();
            }

            //设置二维码容错级别：H
            Map<EncodeHintType,Object> hints = new HashMap<EncodeHintType, Object>();
            hints.put(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.H);
            
            BitMatrix bitMatrix = new MultiFormatWriter().encode(content, BarcodeFormat.QR_CODE, 640, 640, hints);

            // 临时文件路径（本地）
            writeToFile(bitMatrix, formatName, file, name);

//            // 上传到图片服务器（供外部访问）
////            imageUri = FDFSClient.uploadFile(code, fileName, 0);
//            CommonsMultipartFile multipartFile = new CommonsMultipartFile(
//                    new DiskFileItem(code, "", false, fileName, 0, null));
//            imageUri = fileStorageService.uploadFile(multipartFile, "qrcode", dir);

            if (imageUri == null) {
                logger.warn("Fail to upload QR picture file to picture server. ");
            }
        } catch (Exception e) {
            e.printStackTrace();
            logger.warn("Can not generate QR code picture. {}", e.getMessage());
        } finally {
//            if (file != null)
//                file.delete();
        }

        return imageUri;
    }

    private static void writeToFile(BitMatrix matrix, String format, File file, String text) throws IOException {
        BufferedImage image = toBufferedImage(matrix);
        if (text != null) {
            pressText(text, image);
        }
        ImageIO.write(image, format, file);
    }

    /**
     * 生成二维码内容<br>
     * 
     * @param matrix
     * @return
     */
    private static BufferedImage toBufferedImage(BitMatrix matrix) {
        int width = matrix.getWidth();
        int height = matrix.getHeight();
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
                image.setRGB(x, y, matrix.get(x, y) == true ? BLACK : WHITE);
            }
        }
        return image;
    }

    /**
     * 给二维码图片加上文字
     */
    public static void pressText(String pressText, BufferedImage image) throws IOException {
        pressText = new String(pressText.getBytes(), "utf-8");
        Graphics g = image.createGraphics();
        g.setColor(Color.BLACK);
        Font font = new Font("宋体", Font.PLAIN, 24);
        FontMetrics metrics = g.getFontMetrics(font);

        // 文字在图片中的坐标 这里设置在中间
        int startX = (WIDTH - metrics.stringWidth(pressText)) / 2;
        int startY = HEIGHT - 40;
        g.setFont(font);
        g.drawString(pressText, startX, startY);
        g.dispose();
    }