好的，我自己找到了答案。这是在页面上居中放置文本的方法：
String title = "This is my wonderful title!"; // Or whatever title you want.int marginTop = 30; // Or whatever margin you want.PDdocument document = new PDdocument();PDPage page = new PDPage()PDPageStreamContent stream = new PDPageContentStream(document, page);PDFont font = PDType1Font.HELVETICA_BOLD; // Or whatever font you want.int fontSize = 16; // Or whatever font size you want.float titleWidth = font.getStringWidth(title) / 1000 * fontSize;float titleHeight = font.getFontDescriptor().getFontBoundingBox().getHeight() / 1000 * fontSize;stream.beginText();stream.setFont(font, fontSize);stream.moveTextPositionByAmount((page.getMediaBox().getWidth() - titleWidth) / 2, page.getMediaBox().getHeight() - marginTop - titleheight);stream.drawString(title);stream.endText();stream.close();
