java PDF转换图片（多张pdf转换成一整张图片）

1. 引入pdf操作相关pom

	<dependency>
            <groupId>org.apache.pdfbox</groupId>
            <artifactId>pdfbox</artifactId>
            <version>2.0.21</version>
        </dependency>

2. 具体代码

    @RequestMapping(params = "fileToImg")
    public void fileToImg(String ossPath, HttpServletResponse response) {
	//endpoint、accessKeyId、secretAccessKey需要改为自己的配置
        OSS ossClient = new OSSClientBuilder().build(OssConfig.endpoint.getName(), OssConfig.accessKeyId.getName(), OssConfig.accessKeySecret.getName());
        OSSObject object = ossClient.getObject(OssBucketEnum.BASEWEB.getBucketName(), ossPath);
        try (PDDocument load = PDDocument.load(object.getObjectContent())) {
            PDFRenderer pdfRenderer = new PDFRenderer(load);
            int resolution = 300;
            ImageType type = ImageType.RGB;
            List<BufferedImage> bufferedImages = Lists.newArrayList();
            for (int i = 0; i < load.getNumberOfPages(); i++) {
                BufferedImage bufferedImage = pdfRenderer.renderImageWithDPI(i, resolution, type);
                bufferedImages.add(bufferedImage);
            }
            BufferedImage image = new BufferedImage(bufferedImages.stream().map(BufferedImage::getWidth).max(Comparator.naturalOrder()).orElse(0),
                    bufferedImages.stream().map(BufferedImage::getHeight).reduce(Integer::sum).orElse(0), BufferedImage.TYPE_INT_RGB);
	    //将多张图片拼接成一张长图
            Graphics2D graphics = image.createGraphics();
	    //每张图片绘画的起始高度
            int currentHeight = 0;
            for (BufferedImage bufferedImage : bufferedImages) {
                graphics.drawImage(bufferedImage, 0, currentHeight, null);
                currentHeight += bufferedImage.getHeight();
            }
            graphics.dispose();
            response.setContentType("image/png");
	    //返回文件名称处理
            String ossFileName = ossPath.split("/")[1];
	    String fileName=URLUtil.encode(ossFileName.substring(0,ossFileName.lastIndexOf("."))+".png");
            response.setHeader("Content-Disposition", "attachment; filename="+ fileName);
            ImageIO.write(image, "png", response.getOutputStream());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }finally {
            Optional.of(ossClient).ifPresent(OSS::shutdown);
        }
    }