PDFLayers添加图片水印java代码

下面是一个使用PDFLayers库添加图片水印的Java代码示例：

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.pdmodel.graphics.optionalcontent.PDOptionalContentGroup;
import org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDOptionalContentProperties;
import org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDOptionalContentState;
import org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDOptionalContentSubGroup;
import org.apache.pdfbox.pdmodel.graphics.optionalcontent.PDVisibilityPolicy;

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class PDFWatermarkExample {
    
    public static void main(String[] args) throws IOException {
        // Load PDF document
        PDDocument document = PDDocument.load(new File("input.pdf"));

        // Load watermark image
        BufferedImage watermarkImage = ImageIO.read(new File("watermark.png"));

        // Create optional content group for watermark
        PDOptionalContentGroup watermarkGroup = new PDOptionalContentGroup("Watermark");
        watermarkGroup.setPrinted(false);
        PDOptionalContentProperties watermarkProperties = new PDOptionalContentProperties();
        watermarkProperties.setGroup(watermarkGroup);
        PDOptionalContentState watermarkState = new PDOptionalContentState();
        watermarkState.setOn(true);
        watermarkProperties.setCurrentState(watermarkState);

        // Add watermark image to each page
        for (PDPage page : document.getPages()) {
            // Create layer for watermark on this page
            PDOptionalContentGroup pageGroup = new PDOptionalContentGroup("Page " + (document.getPages().indexOf(page) + 1));
            pageGroup.setPrinted(false);
            PDOptionalContentProperties pageProperties = new PDOptionalContentProperties();
            pageProperties.setGroup(pageGroup);
            PDOptionalContentState pageState = new PDOptionalContentState();
            pageState.setOn(true);
            pageProperties.setCurrentState(pageState);

            // Add layer to page content
            PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true);
            contentStream.beginOptionalContent(pageGroup);

            // Add watermark image to layer
            PDImageXObject watermarkXObject = PDImageXObject.createFromFileByContent(watermarkImage, document);
            contentStream.drawImage(watermarkXObject, 0, 0, page.getMediaBox().getWidth(), page.getMediaBox().getHeight());

            contentStream.endOptionalContent();
            contentStream.close();
        }

        // Save document
        document.save(new File("output.pdf"));
        document.close();
    }
}

此代码将加载名为“input.pdf”的PDF文档，并将名为“watermark.png”的图像作为水印添加到每个页面上。它使用PDFLayers库来创建可选内容组和层，并将水印图像添加到正确的层中。最后，它将保存修改后的文档，命名为“output.pdf”。