使用 Apache PDFBox 将图像添加到 PDF 时出现空页问题

Question

I am using this code: https://www.tutorialspoint.com/pdfbox/pdfbox_inserting_image.htm

To help me add an image to an existing PDF. The problem is that the file it creates is a blank page with only the image on it.

Here is my code:

public void signPDF(PdfDTO pdfDTO) throws IOException{
        //Loading an existing document
        File file = new File(getAbsolutePdfPath(pdfDTO));
        PDDocument doc = PDDocument.load(file);

        //Retrieving the page
        PDPage page = doc.getPage(0);

        //a test to ensure the doc is loading correctly
        PDDocument testDoc = new PDDocument();
        testDoc.addPage(page);
        testDoc.save("C:" + File.separator + "Users" + File.separator + "kdotson" + File.separator + "Documents" + File.separator + "test.pdf");
        testDoc.close(); //this file is good so I know the doc is loading correctly

        //Creating PDImageXObject object
        PDImageXObject pdImage = PDImageXObject.createFromFile("C://test_images/signature.pdf", doc);

        //creating the PDPageContentStream object
        PDPageContentStream contents = new PDPageContentStream(doc, page);

        //Drawing the image in the PDF document
        contents.drawImage(pdImage, 0, 0);

        //Closing the PDPageContentStream object
        contents.close();

        //Saving the document
        doc.save(new File(getSignedPdfLocation(pdfDTO))); //the created file has the image on it, so I know the image is loading correctly

        //Closing the document
        doc.close();
    }

As far as I can tell, what I'm doing should work, and I don't get any errors, so what gives?

Answer 1

Please also have a look at the JavaDocs and sources of the library you try to work with. You create a PDPageContentStream :

PDPageContentStream contents = new PDPageContentStream(doc, page);

This conductor is documented to overwrite all existing content streams of this page :

/**
 * Create a new PDPage content stream. This constructor overwrites all existing content streams
 * of this page.
 *
 * @param document The document the page is part of.
 * @param sourcePage The page to write the contents to.
 * @throws IOException If there is an error writing to the page contents.
 */
public PDPageContentStream(PDDocument document, PDPage sourcePage) throws IOException

Thus, you have to use a different constructor which keeps the current page contents, eg

/**
 * Create a new PDPage content stream.
 *
 * @param document The document the page is part of.
 * @param sourcePage The page to write the contents to.
 * @param appendContent Indicates whether content will be overwritten, appended or prepended.
 * @param compress Tell if the content stream should compress the page contents.
 * @param resetContext Tell if the graphic context should be reset. This is only relevant when
 * the appendContent parameter is set to {@link AppendMode#APPEND}. You should use this when
 * appending to an existing stream, because the existing stream may have changed graphic
 * properties (e.g. scaling, rotation).
 * @throws IOException If there is an error writing to the page contents.
 */
public PDPageContentStream(PDDocument document, PDPage sourcePage, AppendMode appendContent,
                           boolean compress, boolean resetContext) throws IOException

Thus

PDPageContentStream contents = new PDPageContentStream(doc, page, AppendMode.APPEND, true, true);

should make your code work as desired.

Alternatively, if you want the image in the background, try

PDPageContentStream contents = new PDPageContentStream(doc, page, AppendMode.PREPEND, true, true);

Beware, though, in certain cases the image won't be visible in the background, eg if the existing content starts with an instruction to fill the whole page area in white. In such a case watermarks must be applied with some kind of transparency atop existing content.