XSLF - Replacing preview image

    @Test
    public void ppt_with_excel() throws IOException, InvalidFormatException {
        FileInputStream fis = new FileInputStream("ppt_with_excel.pptx");
        XMLSlideShow ppt = new XMLSlideShow(fis);
        fis.close();

        XSLFSlide sl = ppt.getSlides().get(0);
        XSLFGraphicFrame gf = (XSLFGraphicFrame)sl.getShapes().get(0);
        XSLFPictureShape ps = gf.getFallbackPicture();
        PackagePart pp = ps.getPictureData().getPackagePart();
        // determine click-me image extension
        File clickMe;
        if ("image/x-emf".equals(pp.getContentType())) {
            clickMe = new File("clickMe.emf");
            // else png, gif, ...
        } else {
            throw new IOException("I don't have 'click me' image for content type "+pp.getContentType());
        }
        OutputStream os = pp.getOutputStream();
        InputStream is = new FileInputStream(clickMe);
        IOUtils.copy(is, os);
        is.close();
        os.close();

        FileOutputStream fos = new FileOutputStream("bla.pptx");
        ppt.write(fos);
        fos.close();

        ppt.close();
    }