场景：

当前需求，前端通过html2canvas将页面报表生成图片下载，可以仍然不满意。
需要java后端将前端传过来的图片生成pdf，并且加密码加水印。

重点：

pdf使用A4大小，但是要考虑。根据A4宽高缩放图片后，图片仍然大于A4长度，此时要对图片进行裁剪（2页，3页…）

maven依赖

<!-- pdf文件水印添加 -->
<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itext7-core</artifactId>
    <version>7.1.4</version>
    <type>pom</type>
</dependency>

controller

    @PostMapping("/addMarkAndPasswordPdf")
    @ApiOperation(value = "文件处理-增加水印及密码--入参为文件", notes = "")
    public void addMarkAndPasswordPdf(@RequestParam("fileStream") MultipartFile[] fileStreams,@RequestParam("filePdfName")String filePdfName,  HttpServletRequest request, HttpServletResponse response) {

        Calendar calendar = Calendar.getInstance();
        String date = calendar.get(Calendar.YEAR) + "-" + (calendar.get(Calendar.MONTH) + 1);

        SysUserEntity uc = (SysUserEntity) request.getAttribute("UC");

        SysUserEntity uc1 = userService.getUserByCode(uc.getUserCode());



        fileProcessService.fileProcessPdf(fileStreams,filePdfName,uc1,response);
    }

service

  @Override
    public void fileProcessPdf(MultipartFile[] imageFiles,String filePdfName, SysUserEntity uc, HttpServletResponse response) {
        response.setHeader("Content-disposition", "attachment;filename=" + filePdfName);
        // 直接用浏览器或者用postman
        response.setContentType("application/pdf");
        response.setCharacterEncoding("utf-8");
        try {
            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
            // 创建PDF文档 加密PDF文档
            PdfWriter writer = new PdfWriter(byteArrayOutputStream,new WriterProperties().setStandardEncryption(
                    // 用户密码
                    uc.getPassword().getBytes(),
                    // 所有者密码
                    uc.getPassword().getBytes(),
                    // 允许的权限
                    EncryptionConstants.ALLOW_PRINTING | EncryptionConstants.ALLOW_COPY,
                    // 加密标准
                    EncryptionConstants.STANDARD_ENCRYPTION_128
            ));
            PdfDocument pdfDoc = new PdfDocument(writer);
            Document document = new Document(pdfDoc);
            // 读取原始图片.按照A4拆分图片，放到pdf
            for(MultipartFile imageFile: imageFiles){
                BufferedImage originalImage = ImageIO.read(imageFile.getInputStream());
                float maxHeight =  (PageSize.A4.getHeight()/PageSize.A4.getWidth())*originalImage.getWidth();
                ArrayList<BufferedImage> cropImageList = cropImageByMaxHeight(originalImage, (int) maxHeight);
                for (BufferedImage bufferedImage : cropImageList) {
                    // 添加图片
                    PdfPage page = pdfDoc.addNewPage();
                    ByteArrayOutputStream ImageOutputStream = new ByteArrayOutputStream();
                    ImageIO.write(bufferedImage, "png", ImageOutputStream);
                    ImageData imageData = ImageDataFactory.create(ImageOutputStream.toByteArray());
                    com.itextpdf.layout.element.Image image = new com.itextpdf.layout.element.Image(imageData);
                    image.setHorizontalAlignment(HorizontalAlignment.CENTER);
                    document.add(image);
                    ImageOutputStream.close();
                    // 循环为页设置水印
                    setPageWatermark(page, pdfDoc,uc.getCname() + ", " + uc.getDeptTwo(),140);
                }
            }

            // 关闭文档以不再写入内容
            document.close();
            pdfDoc.close();
            writer.close();
            // 将PDF写入响应输出流
            response.getOutputStream().write(byteArrayOutputStream.toByteArray());
            response.getOutputStream().flush();
            byteArrayOutputStream.close();
        } catch (Exception e) {
            e.printStackTrace();
            log.error(e.getMessage());
        }
    }

    /***
     * 为PDF页绘画水印
     * @param pdfPage PDF页对象
     * @param msg 水印信息
     * @param interval 水印间隔
     * @throws IOException 这里的异常是无法获取字体异常
     */
    public static void setPageWatermark(PdfPage pdfPage,PdfDocument pdfDoc, String msg, int interval) throws IOException {
        // 通过PDF页来构建画布
        PdfCanvas pdfCanvas = new PdfCanvas(pdfPage);
        // 中文显示字体
//        PdfFont font = PdfFontFactory.createFont("STSong-Light", "UniGB-UCS2-H");
        float width = pdfPage.getPageSize().getWidth();
        float height = pdfPage.getPageSize().getHeight();
        // 开始绘画水印
        for (int x = 0; x < pdfPage.getPageSize().getWidth(); x += interval) {
            for (int y = 0; y < pdfPage.getPageSize().getHeight(); y += interval) {
                Canvas canvas = new Canvas(pdfCanvas, pdfDoc, new Rectangle(0, 0, width, height))
                        // 颜色和透明度
                        .setFontColor(ColorConstants.GRAY, .2f)
                        // 文字样式
//                        .setFont(font)
                        // 字体大小（具体可以改）
                        .setFontSize(20)
                        .showTextAligned(msg, x, y, TextAlignment.CENTER,
                                VerticalAlignment.MIDDLE, 19.5f);
                canvas.close();
            }
        }
        // 释放画布。使用完画布后，请使用此方法。
        pdfCanvas.release();
    }



    /**
     * 将图片进行裁剪
     *
     * @param originalImage
     * @param maxHeight
     * @return
     */
    public static ArrayList<BufferedImage> cropImageByMaxHeight(BufferedImage originalImage, int maxHeight) {
        ArrayList<BufferedImage> croppedImages = new ArrayList<>();
        int originalHeight = originalImage.getHeight();
        int numImages = originalHeight / maxHeight;
        int remainder = originalHeight % maxHeight;

        for (int i = 0; i < numImages; i++) {
            int y = i * maxHeight;
            BufferedImage croppedImage = originalImage.getSubimage(0, y, originalImage.getWidth(), maxHeight);
            croppedImages.add(croppedImage);
        }

        // 处理剩余高度（如有）
        if (remainder > 0) {
            int y = numImages * maxHeight;
            BufferedImage croppedImage = originalImage.getSubimage(0, y, originalImage.getWidth(), remainder);
            croppedImages.add(croppedImage);
        }

        return croppedImages;
    }

成果：