Java中实现给PDF文件添加水印的功能

在Java中，可以使用Apache PDFBox库来给PDF文件添加水印。以下是一个简单的例子，展示了如何实现这个功能：

首先，确保你的项目中包含了PDFBox依赖。如果你使用Maven，可以添加以下依赖：

<dependency>
    <groupId>org.apache.pdfbox</groupId>
    <artifactId>pdfbox</artifactId>
    <version>2.0.24</version>
</dependency>

然后，使用以下Java代码来给PDF文件添加水印：

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageContentStream;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.text.PDFTextStripperByArea;
 
import java.awt.geom.Rectangle2D;
import java.io.File;
import java.io.IOException;
 
public class WatermarkPDF {
    public static void addImageWatermark(String pdfPath, String imagePath, String outputPath) throws IOException {
        try (PDDocument document = PDDocument.load(new File(pdfPath))) {
            PDImageXObject pdImage = PDImageXObject.createFromFile(imagePath, document);
            PDFTextStripperByArea stripper = new PDFTextStripperByArea();
            stripper.setSortByPosition(true);
            for (PDPage page : document.getPages()) {
                PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true, true);
                contentStream.saveGraphicsState();
                contentStream.beginText();
                contentStream.setFont(stripper.getFonts().get(0), 12);
                Rectangle2D.Float rect = new Rectangle2D.Float(0, 0, page.getMediaBox().getWidth(), page.getMediaBox().getHeight());
                contentStream.drawString(stripper.getTextForRegion(rect), 0, 0);
                contentStream.endText();
                contentStream.restoreGraphicsState();
                // Define the transform for the watermark
                PDImageXObject imageXObject = pdImage;
                contentStream.drawImage(imageXObject, 0, page.getMediaBox().getHeight() - imageXObject.getHeight(), imageXObject.getWidth(), imageXObject.getHeight());
                contentStream.close();
            }
            document.save(outputPath);
        }
    }
 
    public static void main(String[] args) {
        try {
            addImageWatermark("input.pdf", "watermark.png", "output.pdf");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

在这个例子中，addImageWatermark方法接受三个参数：pdfPath是待添