iText7处理水印

依赖包

使用itext7需要引入以下依赖包

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itext7-core</artifactId>
    <version>7.1.8</version>
    <type>pom</type>
</dependency>

处理水印方法一

生成水印

public void WatermarkPDF(String sourceFile, String destinationPath) throws IOException {
        float watermarkTrimmingRectangleWidth = 300;
        float watermarkTrimmingRectangleHeight = 300;

        float formWidth = 300;
        float formHeight = 300;
        float formXOffset = 0;
        float formYOffset = 0;

        float xTranslation = 50;
        float yTranslation = 25;

        double rotationInRads = Math.PI/3;

        PdfFont font = PdfFontFactory.createFont(FontConstants.TIMES_ROMAN);
        float fontSize = 50;

        PdfDocument pdfDoc = new PdfDocument(new PdfReader(sourceFile), new PdfWriter(destinationPath));
        int numberOfPages = pdfDoc.getNumberOfPages();
        PdfPage page = null;

        for (int i = 1; i <= numberOfPages; i++)
        {
            page = pdfDoc.getPage(i);
            Rectangle ps = page.getPageSize();

            //Center the annotation
            float bottomLeftX = ps.getWidth()/2 - watermarkTrimmingRectangleWidth/2;
            float bottomLeftY = ps.getHeight()/2 - watermarkTrimmingRectangleHeight/2;
            Rectangle watermarkTrimmingRectangle = new Rectangle(bottomLeftX, bottomLeftY, watermarkTrimmingRectangleWidth, watermarkTrimmingRectangleHeight);

            PdfWatermarkAnnotation watermark = new PdfWatermarkAnnotation(watermarkTrimmingRectangle);

            //Apply linear algebra rotation math
            //Create identity matrix
            AffineTransform transform = new AffineTransform();//No-args constructor creates the identity transform
            //Apply translation
            transform.translate(xTranslation, yTranslation);
            //Apply rotation
            transform.rotate(rotationInRads);

            PdfFixedPrint fixedPrint = new PdfFixedPrint();
            watermark.setFixedPrint(fixedPrint);
            //Create appearance
            Rectangle formRectangle = new Rectangle(formXOffset, formYOffset, formWidth, formHeight);

            //Observation: font XObject will be resized to fit inside the watermark rectangle
            PdfFormXObject form = new PdfFormXObject(formRectangle);
            PdfExtGState gs1 = new PdfExtGState().setFillOpacity(0.6f);
            PdfCanvas canvas = new PdfCanvas(form, pdfDoc);

            float[] transformValues = new float[6];
            transform.getMatrix(transformValues);
            canvas.saveState()
                    .beginText().setColor(ColorConstants.GRAY, true).setExtGState(gs1)
                    .setTextMatrix(transformValues[0], transformValues[1], transformValues[2], transformValues[3], transformValues[4], transformValues[5])
                    .setFontAndSize(font, fontSize)
                    .showText("watermark text")
                    .endText()
                    .restoreState();

            canvas.release();

            watermark.setAppearance(PdfName.N, new PdfAnnotationAppearance(form.getPdfObject()));
            watermark.setFlags(PdfAnnotation.PRINT);

            page.addAnnotation(watermark);

        }
        page.flush();
        pdfDoc.close();
    }

这种方法生成的水印不可编辑，不可复制

移除水印

在上述方法生成水印的前提下，可使用以下方法来移除水印

public void RemovetWatermarkPDF(String sourceFile, String destinationPath) throws IOException {
        PdfDocument pdfDoc = new PdfDocument(new PdfReader(sourceFile), new PdfWriter(destinationPath));
        int numberOfPages = pdfDoc.getNumberOfPages();

        for (int i = 1; i <= numberOfPages; i++)
        {
            // PdfAnnotation
            PdfDictionary pageDict = pdfDoc.getPage(i).getPdfObject();
            PdfArray annots = pageDict.getAsArray(PdfName.Annots);
            for (int j = 0; j < annots.size(); j++)
            {
                PdfDictionary annotation = annots.getAsDictionary(j);
                if (PdfName.Watermark.equals(annotation.getAsName(PdfName.Subtype)))
                {
                    annotation.clear();
                }
            }
        }
        pdfDoc.close();
    }

这里添加移除的水印，和pdf正文不在同一层画布，因此可以进行移除操作。

方法二

我们也可以使用以下方法来生成水印

    public void manipulatePdf(String dest) throws Exception {
        PdfDocument pdfDoc = new PdfDocument(new PdfReader(SRC), new PdfWriter(dest));
        Document doc = new Document(pdfDoc);
        PdfFont font = PdfFontFactory.createFont(StandardFonts.HELVETICA);
        Paragraph paragraph = new Paragraph("My")
                .setFont(font)
                .setFontSize(30);
        ImageData img = ImageDataFactory.create(IMG);

        float w = img.getWidth();
        float h = img.getHeight();

        PdfExtGState gs1 = new PdfExtGState().setFillOpacity(0.5f);

        // Implement transformation matrix usage in order to scale image
        for (int i = 1; i <= pdfDoc.getNumberOfPages(); i++) {

            PdfPage pdfPage = pdfDoc.getPage(i);
            Rectangle pageSize = pdfPage.getPageSizeWithRotation();

            // When "true": in case the page has a rotation, then new content will be automatically rotated in the
            // opposite direction. On the rotated page this would look as if new content ignores page rotation.
            pdfPage.setIgnorePageRotationForContent(true);

            float x = (pageSize.getLeft() + pageSize.getRight()) / 2;
//            float y = (pageSize.getTop() + pageSize.getBottom()) / 2;
            float y = pageSize.getTop() -70;
            PdfCanvas over = new PdfCanvas(pdfDoc.getPage(i));
            over.saveState();
            over.setExtGState(gs1);
            if (i % 2 == 1) {
                doc.showTextAligned(paragraph, x, y, i, TextAlignment.CENTER, VerticalAlignment.TOP, 0);
            } else {
                over.addImageWithTransformationMatrix(img, w, 0, 0, h, x - (w / 2), y - (h / 2), false);
            }
            over.restoreState();
        }

        doc.close();
    }

在Document中，有paragraph、div等元素，可用来在pdf画布上生成pdf要素。使用paragraph可以在pdf中创建一段文字，这里showTextAligned方法创建了div，效果类似paragraph。因此这种方法中生成的水印，等效于pdf正文，只是在样式以及透明度上做了区分。通过软件编辑pdf可发现这里的水印可被复制。
因为这里的水印和正文在同一图层中因此，不能被移除。