private static int interval = 30;

    public static void waterMark(String inputFile,String outputFile, String waterMarkName) {

        try {

            PdfReader reader = new PdfReader(inputFile);

            PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(outputFile));

            //这里的字体设置比较关键，这个设置支持中文的写法

            BaseFont base = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H",   BaseFont.EMBEDDED);  //使用系统字体

            Rectangle pageRect = null;

            PdfGState gs = new PdfGState();

            //设置透明度

            gs.setFillOpacity(0.3f);

            gs.setStrokeOpacity(0.3f);

            int total = reader.getNumberOfPages() + 1;

            JLabel label = new JLabel();

            FontMetrics metrics;

            int textH = 0;

            int textW = 0;

            label.setText(waterMarkName);

            metrics = label.getFontMetrics(label.getFont());

            textH = metrics.getHeight();

            textW = metrics.stringWidth(label.getText());

            PdfContentByte under;

            for (int i = 1; i < total; i++) {

                pageRect = reader.getPageSizeWithRotation(i);

                under = stamper.getOverContent(i);

                under.saveState();

                under.setGState(gs);

                under.beginText();

                under.setFontAndSize(base, 30); //控制字体间宽度

                // 水印文字成30度角倾斜

                for (int height = interval + textH; height < pageRect.getHeight();  height = height + textH*8) {

                    for (int width = interval + textW; width < pageRect.getWidth() + textW;  width = width + textW*4) {

                        under.showTextAligned(Element.ALIGN_LEFT , waterMarkName, width - textW,

                                height - textH, 30);  }  }

                // 添加水印文字

                under.endText();

                }

            //关闭流

            stamper.close();

            reader.close();

            } catch (Exception e) {

                e.printStackTrace();

            }

        }

private static final float IAMGE_HEIGHT = 110f; // 水印图片的的高度

    private static final float IAMGE_WIDTH = 110f; // 水印图片的的宽度

    public static void addPdfMark(String pdfPath,String logoPath, String outPath) throws Exception {

        PdfReader reader = new PdfReader(pdfPath, "PDF".getBytes());

        // 如果是web项目，直接下载应该放到response的流里面

        // PdfStamper stamp = new PdfStamper(reader,response.getOutputStream());

        // 添加水印之后的pdf文件

        PdfStamper stamp = new PdfStamper(reader, new FileOutputStream(outPath));

        int pageSize = reader.getNumberOfPages();

        float pageHeight = reader.getPageSize(1).getHeight();

        float pageWidth = reader.getPageSize(1).getWidth();

        try {

            // 每两行显示两个 左边一个，右边一个

            int lineNum = (int) (pageHeight / IAMGE_HEIGHT); // 行数

            int middleY = (int) pageWidth / 2;

            for (int i = 1; i <= pageSize; i++) {

                for (int j = 0, k = 0; j < lineNum; j = j + 4, k++) {

                    Random random = new Random();

                    // 放入水印

                    Image img = Image.getInstance(logoPath);

                    img.scaleAbsolute(IAMGE_WIDTH, IAMGE_HEIGHT * 184 / 455);

                    // 将水印显示到最底层

                    img.setAlignment(Image.UNDERLYING);

                    int trueY;

                    while (true) {

                        trueY = random.nextInt(middleY);

                        if (trueY > IAMGE_WIDTH / 2 && trueY < (middleY - IAMGE_WIDTH)) {

                            break;

                        }

                    }

                    // 水印的位置

                    img.setAbsolutePosition(trueY, j * IAMGE_HEIGHT + (float) random.nextInt((int) IAMGE_HEIGHT) - (k % 2) * 10);

                    // 旋转 角度

                    img.setRotationDegrees(random.nextInt(360));

                    PdfContentByte under = stamp.getUnderContent(i);

                    PdfGState gs = new PdfGState();

                    // 设置透明度为0.5

                    gs.setFillOpacity(0.5f);

                    under.setGState(gs);

                    under.addImage(img);

                    while (true) {

                        trueY = random.nextInt(middleY) + middleY;

                        if (trueY > middleY + IAMGE_WIDTH / 2 && trueY < (2 * middleY - IAMGE_WIDTH)) {

                            break;

                        }

                    }

                    // 水印的位置

                    img.setAbsolutePosition(trueY, j * IAMGE_HEIGHT + (float) random.nextInt((int) IAMGE_HEIGHT) - (k % 2) * 10);

                    // 旋转角度

                    img.setRotationDegrees(random.nextInt(360));

                    under.addImage(img);

                }

            }

        } catch (Exception e) {

            throw e;

        } finally {

            stamp.close();

            reader.close();

        }

public static void main(String[] args) throws Exception {

        waterMark("xxx.pdf", "yyy.pdf", "测试工程");

        //addPdfMark("xxx.pdf","image.png","yyy.xml");

        System.out.println("结束");

    }

    }