我如何在PDF中添加水印，并使用“规模相对于目标页面”

Question

我使用基于TransparentWatermark例如一个例子，

http://developers.itextpdf.com/examples/stamping-content-existing-pdfs/clone-watermark-examples

，但我似乎无法找到一个方法或者与Adobe设置中的“添加水印”关联的“相对于目标页面的缩放比例”相关的选项。

有人可以指出我吗？

Answer 1

已经开始创建Textwatermark示例的变体，该变体缩放水印以覆盖总页面面积的百分比。从本质上讲，它是寻找合适的标度变换，使的线性代数问题，确保所有其他平移和旋转是正确的

package Stackoverflow.ScalingWatermark; 

import com.itextpdf.io.IOException; 
import com.itextpdf.io.font.FontConstants; 
import com.itextpdf.kernel.color.Color; 
import com.itextpdf.kernel.color.DeviceCmyk; 
import com.itextpdf.kernel.events.Event; 
import com.itextpdf.kernel.events.IEventHandler; 
import com.itextpdf.kernel.events.PdfDocumentEvent; 
import com.itextpdf.kernel.font.PdfFont; 
import com.itextpdf.kernel.font.PdfFontFactory; 
import com.itextpdf.kernel.geom.AffineTransform; 
import com.itextpdf.kernel.geom.Rectangle; 
import com.itextpdf.kernel.pdf.PdfDocument; 
import com.itextpdf.kernel.pdf.PdfPage; 
import com.itextpdf.kernel.pdf.PdfWriter; 
import com.itextpdf.kernel.pdf.canvas.PdfCanvas; 
import com.itextpdf.kernel.pdf.xobject.PdfFormXObject; 
import com.itextpdf.layout.Document; 
import com.itextpdf.layout.border.SolidBorder; 
import com.itextpdf.layout.element.AreaBreak; 
import com.itextpdf.layout.element.Div; 
import com.itextpdf.layout.element.Paragraph; 
import com.itextpdf.layout.property.AreaBreakType; 
import com.itextpdf.licensekey.LicenseKey; 

import java.io.File; 

public class ScalingWatermark { 
    public static String DEST = "target/output/Stackoverflow/ScalingWatermark/output.pdf"; 
    public static String LICENSE = "src/test/resources/skeleton-itextkey.xml"; 
    public static String[] CONTENT = {"I have seen the face of sorrow", "She looks away in the distance", 
      "Across all these bridges", "From whence I came", 
      "And those spans, trussed and arched", "Hold up our lives as we go back again", 
      "To how we thought then", "To how we thought we thought then", 
      "I have seen sorrow's face", "But she is ever turned away", 
      "And her words leave me blind", "Her eyes make me mute", 
      "I do not understand what she says to me", "I do not know if to obey", 
      "Or attempt a flood of tears", "I have seen her face", 
      "She does not speak", "She does not weep", 
      "She does not know me", "For I am but a stone fitted in place", 
      "On the bridge where she walks", "―Lay of the Bridgeburners", 
      "Toc the Younger" 
    }; 

    public static void main(String[] args) throws IOException, java.io.IOException { 
     LicenseKey.loadLicenseFile(LICENSE); 
     File file = new File(DEST); 
     file.getParentFile().mkdirs(); 
     new ScalingWatermark().createPdf(DEST); 
    } 

    public void createPdf(String dest) throws IOException, java.io.IOException { 
     PdfWriter writer = new PdfWriter(dest); 
     PdfDocument pdfDoc = new PdfDocument(writer); 
     Document doc = new Document(pdfDoc); 
     pdfDoc.addEventHandler(PdfDocumentEvent.END_PAGE, 
       new TextWatermark()); 
     addContent(doc); 
     doc.add(new AreaBreak(AreaBreakType.NEXT_PAGE)); 
     addContent(doc); 
     doc.close(); 

    } 

    private void addContent(Document doc) { 
     Div div = new Div().setBorder(new SolidBorder(1)); 
     for (String line : CONTENT) { 
      Paragraph p = new Paragraph(line).setMarginBottom(0).setMarginTop(0).setMarginLeft(5f); 
      div.add(p); 
     } 
     doc.add(div); 
    } 


    protected class TextWatermark implements IEventHandler { 

     Color lime, blue; 
     PdfFont helvetica; 

     protected TextWatermark() throws java.io.IOException { 
      helvetica = PdfFontFactory.createFont(FontConstants.HELVETICA); 
      lime = new DeviceCmyk(0.208f, 0, 0.584f, 0); 
      blue = new DeviceCmyk(0.445f, 0.0546f, 0, 0.0667f); 
     } 

     @Override 
     public void handleEvent(Event event) { 
      PdfDocumentEvent docEvent = (PdfDocumentEvent) event; 
      PdfDocument pdf = docEvent.getDocument(); 
      PdfPage page = docEvent.getPage(); 
      int pageNumber = pdf.getPageNumber(page); 
      Rectangle pageSize = page.getPageSize(); 

      //Scale to a percentage of the page area 
      float scalingAreaReq = pageNumber % 2 == 0 ? 0.75f : 0.50f; 
      //Calculate scaling and x-y positioning 
      float scalingFactor = (float) Math.sqrt(scalingAreaReq); 
      AffineTransform scaleTf = new AffineTransform(); 
      //Calculation based on centering the watermark 
      float xPos = ((1 - scalingFactor) * pageSize.getWidth())/2; 
      float yPos = ((1 - scalingFactor) * pageSize.getHeight())/2; 
      //Add translation to our transformation 
      scaleTf.translate(xPos,yPos); 
      //Add scaling to our transformation 
      scaleTf.scale(scalingFactor, scalingFactor); 

      //Use values from calculation 
      PdfCanvas pdfCanvas = new PdfCanvas(page.newContentStreamBefore(), page.getResources(), pdf); 
      PdfFormXObject watermarkAsXObject = createWatermarkXObject(pageNumber, pageSize, pdf); 
      pdfCanvas.saveState() 
        //Apply scaling 
        .concatMatrix(scaleTf) 
        //Insert watermark 
        .addXObject(watermarkAsXObject, 0, 0) 
        .restoreState(); 

      pdfCanvas.release(); 
     } 


     private PdfFormXObject createWatermarkXObject(int pageNumber, Rectangle bBox, PdfDocument pdfDoc) { 
      PdfFormXObject xObject = new PdfFormXObject(bBox); 
      PdfCanvas pdfCanvas = new PdfCanvas(xObject, pdfDoc); 
      int fontSize = 40; 
      float margin = 100; 

      //Paint the area that the watermark occupies 
      pdfCanvas.saveState() 
        .setFillColor(pageNumber % 2 == 1 ? lime : blue) 
        .rectangle(bBox.getLeft(), bBox.getBottom(), 
          bBox.getWidth(), bBox.getHeight()) 
        .fill().restoreState(); 

      //Translation and rotation to center the watermark text 
      AffineTransform rotationAndTranslation = AffineTransform.getTranslateInstance(bBox.getWidth()/2- margin,bBox.getHeight()/2); 
      AffineTransform rotation = AffineTransform.getRotateInstance(Math.PI/4); 
      rotationAndTranslation.concatenate(rotation); 

      //Create the actual text 
      pdfCanvas.saveState() 
        .beginText() 
        .setFontAndSize(helvetica, fontSize) 
        .setFillColor(pageNumber % 2 != 1 ? lime : blue) 
        .setTextMatrix(rotationAndTranslation) 
        .showText("Watermark") 
        .endText() 
        .restoreState(); 

      pdfCanvas.release(); 

      return xObject; 

     } 
    } 
}