java - 在 Java 中将整个 JDialog UI 转换为 PDF 文件

Question

我想将 Enite Jframe UI 转换为 PDF 文件。我在这里得到了一份代码表格。但它抛出异常说

Error in Print Module The document has no pages.
ExceptionConverter: java.io.IOException: The document has no pages.
        at com.itextpdf.text.pdf.PdfPages.writePageTree(PdfPages.java:113)
        at com.itextpdf.text.pdf.PdfWriter.close(PdfWriter.java:1221)
        at com.itextpdf.text.pdf.PdfDocument.close(PdfDocument.java:810)
        at com.itextpdf.text.Document.close(Document.java:416)

我的代码用于打印 JFrame

public static void PrintFrameToPDF(JDialog bill)
    {
    try {

            Document d = new Document();
            PdfWriter writer = PdfWriter.getInstance(d, new FileOutputStream ("sample.pdf"));
            d.open ();

            PdfContentByte cb = writer.getDirectContent( );
            PdfTemplate template = cb.createTemplate(bill.getWidth(),bill.getHeight());
            Graphics2D g2d = template.createGraphics(bill.getWidth(),bill.getHeight());
            bill.print(g2d);
            bill.addNotify();
            bill.validate();


            d.close ();
        }
        catch(Exception e)  {
          System.out.println("Error in Print Module " + e.getMessage());
          e.printStackTrace();
        }

调用 PDF 的用法 PrintModule.PrintFrameToPDF(this);// 当前 JFrame 表单中存在此行