spring boot PDF并添加水印、签名和盖章

Spring Boot 可以使用 iText 库来实现 PDF 的添加水印、签名和盖章。以下是基本步骤：

1. 导入 iText 和 BC 签名库的 Maven 依赖。

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.13</version>
</dependency>
<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcprov-jdk15on</artifactId>
    <version>1.61</version>
</dependency>

2. 定义并创建 PDF 文档对象。

Document document = new Document();
PdfWriter writer = PdfWriter.getInstance(document, out);
document.open();

3. 添加文字水印。

PdfContentByte canvas = writer.getDirectContentUnder();
Font font = new Font(FontFamily.HELVETICA, 52, Font.BOLD, new GrayColor(0.75f));
Phrase phrase = new Phrase("WATERMARK", font);
ColumnText.showTextAligned(canvas, Element.ALIGN_CENTER, phrase, 297, 421, 45);

4. 添加图片水印。

Image image = Image.getInstance("path/to/image.png");
image.scaleAbsolute(400, 400);
image.setAbsolutePosition(100, 100);
document.add(image);

5. 添加数字签名。

KeyStore ks = KeyStore.getInstance("PKCS12");
ks.load(new FileInputStream("path/to/keystore.p12"), "keystorePassword".toCharArray());
String alias = (String) ks.aliases().nextElement();
PrivateKey privateKey = (PrivateKey) ks.getKey(alias, "keyPassword".toCharArray());
Certificate[] chain = ks.getCertificateChain(alias);

PdfReader reader = new PdfReader("path/to/pdf");
PdfStamper stamper = PdfStamper.createSignature(reader, out, '\0');
PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
appearance.setReason("Reason for signing");
appearance.setLocation("Location of signing");
appearance.setCertificationLevel(PdfSignatureAppearance.CERTIFIED_FORM_FILLING_AND_ANNOTATIONS);
appearance.setVisibleSignature(new Rectangle(36, 748, 144, 780), 1, "signature");

ExternalSignature es = new PrivateKeySignature(privateKey, "SHA-256", "BC");
ExternalDigest digest = new BouncyCastleDigest();
MakeSignature.signDetached(appearance, digest, es, chain, null, null, null, 0, MakeSignature.CryptoStandard.CMS);

stamper.close();

6. 添加印章。

PdfReader reader = new PdfReader("path/to/pdf");
PdfStamper stamper = new PdfStamper(reader, out);
PdfContentByte canvas = stamper.getOverContent(1);
Image image = Image.getInstance("path/to/stamp.png");
image.scaleAbsolute(150, 150);
image.setAbsolutePosition(200, 200);
canvas.addImage(image);
stamper.close();

7. 关闭文档和输出流。

document.close();
out.close();

以上步骤仅作为示例，具体实现可能因为证书类型、签名算法、水印、印章等不同而有所区别。