Java实现PDF加水印功能：技术解析与实践指南

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

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDPageContentStream;
import org.apache.pdfbox.pdmodel.font.PDType1Font;

import java.io.File;
import java.io.IOException;

public class PdfBoxWatermark {
    public static void main(String[] args) throws IOException {
        // 读取原始PDF文件
        PDDocument document = PDDocument.load(new File("original.pdf"));

        // 遍历PDF中的所有页面
        for (int i = 0; i < document.getNumberOfPages(); i++) {
            PDPage page = document.getPage(i);
            PDPageContentStream contentStream = new PDPageContentStream(document, page, PDPageContentStream.AppendMode.APPEND, true, true);

            // 设置字体和字号
            contentStream.setFont(PDType1Font.HELVETICA_BOLD, 36);

            // 设置透明度
            contentStream.setNonStrokingColor(200, 200, 200);

            // 添加文本水印
            contentStream.beginText();
            contentStream.newLineAtOffset(100, 100); // 设置水印位置
            contentStream.showText("Watermark"); // 设置水印内容
            contentStream.endText();

            contentStream.close();
        }

        // 保存修改后的PDF文件
        document.save(new File("output.pdf"));
        document.close();
    }
}

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13</version>
</dependency>

import com.itextpdf.text.*;
import com.itextpdf.text.pdf.*;

import java.io.FileOutputStream;
import java.io.IOException;

public class ItextWatermark {
    public static void main(String[] args) throws IOException, DocumentException {
        // 读取原始PDF文件
        PdfReader reader = new PdfReader("original.pdf");
        PdfStamper stamper = new PdfStamper(reader, new FileOutputStream("output.pdf"));

        // 获取PDF中的页数
        int pageCount = reader.getNumberOfPages();

        // 添加水印
        for (int i = 1; i <= pageCount; i++) {
            PdfContentByte contentByte = stamper.getUnderContent(i); // 或者getOverContent()
            contentByte.beginText();
            contentByte.setFontAndSize(BaseFont.createFont(), 36f);
            contentByte.setColorFill(BaseColor.LIGHT_GRAY);
            contentByte.showTextAligned(Element.ALIGN_CENTER, "Watermark", 300, 400, 45);
            contentByte.endText();
        }

        // 保存修改后的PDF文件并关闭文件流
        stamper.close();
        reader.close();
    }
}

gs -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=output.pdf -c "newpath /Helvetica-Bold findfont 36 scalefont setfont 0.5 setgray 200 200 moveto (Watermark) show showpage" original.pdf

<dependency>
    <groupId>e-iceblue</groupId>
    <artifactId>free-spire-pdf-for-java</artifactId>
    <version>1.9.6</version>
</dependency>

import com.spire.pdf.*;

public class FreeSpirePdfWatermark {
    public static void main(String[] args) {
        // 读取原始PDF文件
        PdfDocument pdf = new PdfDocument();
        pdf.loadFromFile("original.pdf");

        // 遍历PDF中的所有页面
        for (int i = 0; i < pdf.getPages().getCount(); i++) {
            PdfPageBase page = pdf.getPages().get(i);

            // 添加文本水印
            PdfWatermark watermark = new PdfWatermark("Watermark");
            watermark.setFont(new PdfFont(PdfFontFamily.Helvetica, 36));
            watermark.setOpacity(0.5f);
            page.getWatermarks().add(watermark);
        }

        // 保存修改后的PDF文件
        pdf.saveToFile("output.pdf");
        pdf.close();
    }
}

<dependency>
    <groupId>com.aspose</groupId>
    <artifactId>aspose-pdf</artifactId>
    <version>21.4</version>
</dependency>

import com.aspose.pdf.*;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;

import java.io.ByteArrayOutputStream;
import java.io.IOException;

@RestController
@RequestMapping("/api/pdf")
public class PdfController {
    @PostMapping("/addTextWatermark")
    public ResponseEntity<byte[]> addTextWatermark(@RequestParam("file") MultipartFile file) throws IOException {
        // 加载PDF文件
        Document pdfDocument = new Document(file.getInputStream());
        TextStamp textStamp = new TextStamp("Watermark");
        textStamp.setWordWrap(true);
        textStamp.setVerticalAlignment(VerticalAlignment.Center);
        textStamp.setHorizontalAlignment(HorizontalAlignment.Center);
        pdfDocument.getPages().get_Item(1).addStamp(textStamp);

        // 保存PDF文件
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        pdfDocument.save(outputStream);
        return ResponseEntity.ok()
                .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"watermarked.pdf\"")
                .contentType(MediaType.APPLICATION_PDF)
                .body(outputStream.toByteArray());
    }
}