如何使用 iText 将图形绘制为 PDF？

我正在尝试完成一个绘制图形并将其写入 PDF 的示例，但我不断收到 PDF 没有页面的错误。如果我在打开后使用 document.add() 添加一些简单的东西，它工作正常，我只是永远看不到图形。这是我的代码：

Document document = new Document();
PdfWriter writer = new PdfWriter();
response.setContentType("application/pdf");
response.setHeader("Content-Disposition",
    " attachment; filename=\"Design.pdf\"");

writer = PdfWriter.getInstance(document, response.getOutputStream());

document.open();    
PdfContentByte cb = writer.getDirectContent();
Graphics2D graphics2D = cb.createGraphics(36, 54);
graphics2D.drawString("Hello World", 36, 54);
graphics2D.dispose();   
document.close();

我是否需要执行其他操作才能将图形添加到文档中，或者我的语法是否不正确？

我不是 IText 专家，但上周我尝试用它画一些圆圈。这是我在测试过程中注意到的：

如果您绘制图形，则必须（或者说当我尝试时我必须这样做）将图形命令“包装”在以以下开头的部分中saveState()并以restoreState()，以及我需要调用fillStroke()-- 如果我不调用fillStroke()然后什么也没画。

Example

private void circle(float x, float y, PdfWriter writer) {
    PdfContentByte canvas = writer.getDirectContent();

    canvas.saveState();
    canvas.setColorStroke(GrayColor.BLACK);
    canvas.setColorFill(GrayColor.BLACK);
    canvas.circle(x, y, 2);
    canvas.fillStroke();

    canvas.restoreState();
}

@Test
public void testPossition() throws DocumentException, IOException {
    OutputStream outputStream = FileUtil.openOutputStream("testPosition.pdf");
    //this is my personal file util, but it does not anything more
    //then creating a file and opening the file stream.

    Document document = new Document(PageSize.A4, 50, 50, 50, 50);
    PdfWriter writer = PdfWriter.getInstance(document, outputStream);
    document.open();

    markPosition(100, 100, writer);
    document.add(new Paragraph("Total: 595 x 842 -- 72pt (1 inch)"));

    document.close();
    outputStream.flush();
    outputStream.close();
}

private void markPosition(float x, float y, PdfWriter writer)
        throws DocumentException, IOException {
    placeChunck("x: " + x + " y: " + y, x, y, writer);
    circle(x, y, writer);
}

 private void placeChunck(String text, float x, float y, PdfWriter writer)
       throws DocumentException, IOException {
    PdfContentByte canvas = writer.getDirectContent();
    BaseFont font = BaseFont.createFont(BaseFont.HELVETICA,
                  BaseFont.CP1252, BaseFont.NOT_EMBEDDED);
    canvas.saveState();
    canvas.beginText();
    canvas.moveText(x, y);
    canvas.setFontAndSize(font, 9);
    canvas.showText(text);
    canvas.endText();
    canvas.restoreState();
}

But PdfContentByte(canvas) 有更多的功能，例如rectangle.