itext實現水印功能

近日要用itext來做水印功能，在網上找了好多資料，但都是把原來的內容覆蓋了，最後找了這種方法，效果不錯


//---------pdf水印-------------
try {   //水印路徑
            PdfReader reader = new PdfReader(filePath_tem);
            PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(filePath));
            //stamper.setEncryption(userPassWord.getBytes(), ownerPassWord
            //.getBytes(), permission, false);
            BaseFont base = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H",
            BaseFont.NOT_EMBEDDED);
            int total = reader.getNumberOfPages() + 1;
       //圖片路徑，位置與大小
            Image image = Image.getInstance(imageFilePath);
            image.setAbsolutePosition(100, 300);
image.scalePercent(100);
                                    PdfContentByte under;
            int j = waterMarkName.length();
            char c = 0;
            int rise = 0;
            for (int i = 1; i < total; i++) {
            rise = 500;
            under = stamper.getUnderContent(i);
            under.addImage(image);
         under.beginText();
            under.setColorFill(Color.CYAN);
            under.setFontAndSize(base, 30);
            if (j >= 15) {
            under.setTextMatrix(200, 120);
            for (int k = 0; k < j; k++) {
            under.setTextRise(rise);
            c = waterMarkName.charAt(k);
            under.showText(c + "");
            rise -= 20;
            }
            } else {
            under.setTextMatrix(180, 100);
            for (int k = 0; k < j; k++) {
            under.setTextRise(rise);
            c = waterMarkName.charAt(k);
            under.showText(c + "");
            rise -= 18;
            }
            }
            under.endText();
            // under.ellipse(250, 450, 350, 550);
            // under.setLineWidth(1f);
            // under.stroke();
            }
            stamper.close();
            } catch (Exception e) {
            e.printStackTrace();
            }