// 生成图片

            PDDocument pd = PDDocument.load(new File(filePath));

            PDFRenderer pdfRenderer = new PDFRenderer(pd);

            BufferedImage combined = null;

            for (int page = 0; page < pd.getNumberOfPages(); ++page)

            {

                BufferedImage bim = pdfRenderer.renderImageWithDPI(page, 96, ImageType.RGB);

                if (page == 0) {

                    combined = bim;

                } else {

                    combined = merge(combined, bim);

                }

            }

            ImageIOUtil.writeImage(combined, filePath + ".png", 96);

            pd.close();

    private static BufferedImage merge(BufferedImage image1, BufferedImage image2) {

        BufferedImage combined = new BufferedImage(

                image1.getWidth(),

                image1.getHeight() + image2.getHeight(),

                BufferedImage.TYPE_INT_RGB);

        Graphics g = combined.getGraphics();

        g.drawImage(image1, 0, 0, null);

        g.drawImage(image2, 0, image1.getHeight(), null);

        g.dispose();

        return combined;

    }