通过itext对PDF嵌入数字证书

###1、新老版本区别简要介绍(话说很多人不知道如何区别) 新老版本最直接的区别就是包命名方式，itext5之前的命名方式为com.lowagie.text，从itext5以后，命名方式改为com.itextpdf.text，通过这个方式最容易判断。

可以直接的看出itext的两个命名方式，咦( ′◔ ‸◔`) 老版本竟然还有那么多人在使用~~~

• itext5之前的版本

• itex- t5之后的版本

###2、itext对第三方构建的依赖 通过itext对pdf做数字证书时候，需要用到第三方的加解密工具包，以itext5.5.5为例，查看其用到的org.bouncycastle(著名的加密码工具)包的版本。

###3、代码样例

/*pom配置文件*/
<dependency>
	<groupId>com.itextpdf</groupId>
	<artifactId>itextpdf</artifactId>
	<version>5.5.5</version>
</dependency>
<dependency>
	<groupId>com.itextpdf</groupId>
	<artifactId>itext-asian</artifactId>
	<version>5.2.0</version>
</dependency>
<dependency>
	<groupId>org.bouncycastle</groupId>
	<artifactId>bcpkix-jdk15on</artifactId>
	<version>1.54</version>
</dependency>
<dependency>
	<groupId>org.bouncycastle</groupId>
	<artifactId>bcprov-jdk15on</artifactId>
	<version>1.54</version>
</dependency>

public static void makeSignature(String src, String dest) {
        BouncyCastleProvider provider = new BouncyCastleProvider();
        Security.addProvider(provider);
        KeyStore ks = null;
        String alias = null;
        PrivateKey pk = null;
        Certificate[] chain = null;
        try {
            ks = KeyStore.getInstance("pkcs12");
            ks.load(new FileInputStream(KEYSTORE), PASSWORD.toCharArray());
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            alias = (String)ks.aliases().nextElement();
            pk = (PrivateKey) ks.getKey(alias, PASSWORD.toCharArray());
            chain = ks.getCertificateChain(alias);
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            PdfReader reader = new PdfReader(src);
            FileOutputStream os = new FileOutputStream(dest);
            PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0');
//PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0', null, true);
//在一份PDF文档中嵌入多个数字证书请参考上面一行注释的代码
            PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
            BaseFont bfChinese = BaseFont.createFont("STSong-Light", "UniGB-UCS2-H", BaseFont.NOT_EMBEDDED);
            appearance.setLayer2Font(new Font(bfChinese, 8, Font.NORMAL));
            appearance.setLayer2Text("\n\n\n   浙 江 X X X X 科 技 有 限 公 司");
            appearance.setReason("签名防伪");
            appearance.setLocation("浙江杭州");  //添加位置信息，可为空
            appearance.setContact("service@yunhetong.net");
            appearance.setVisibleSignature(new Rectangle(380, 755, 512, 812), reader.getNumberOfPages(), "sig");
            ExternalDigest digest = new BouncyCastleDigest();
            ExternalSignature signature = new PrivateKeySignature(pk, DigestAlgorithms.SHA256, provider.getName());
            MakeSignature.signDetached(appearance, digest, signature, chain, null, null, null, 0, MakeSignature.CryptoStandard.CMS);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

这个也是参考官方样例代码进行修改的~