使用 Apache PDFBox 將圖像添加到 PDF 時出現空頁問題

Question

我正在使用此代碼： https : //www.tutorialspoint.com/pdfbox/pdfbox_inserting_image.htm

幫助我將圖像添加到現有 PDF。 問題是它創建的文件是一個空白頁，上面只有圖像。

這是我的代碼：

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();
    }

據我所知，我正在做的事情應該可以工作，而且我沒有收到任何錯誤，那么有什么用呢？

Answer 1

還請查看您嘗試使用的庫的 JavaDoc 和源代碼。 您創建一個PDPageContentStream ：

PDPageContentStream contents = new PDPageContentStream(doc, page);

該指揮被記錄為覆蓋此頁面的所有現有內容流：

/**
 * 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

因此，您必須使用不同的構造函數來保留當前頁面內容，例如

/**
 * 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

因此

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

應該使您的代碼按需要工作。

或者，如果您想要背景中的圖像，請嘗試

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

但是請注意，在某些情況下，圖像在背景中不可見，例如，如果現有內容以用白色填充整個頁面區域的指令開始。 在這種情況下，水印必須以某種透明度應用在現有內容之上。