最近在研究Itext对pdf进行签章，记录一下。
可参照：http://developers.itextpdf.com/examples/security-itext5/digital-signatures-white-paper中的例子
一。准备相关文件：
1.背景色为空的印章图片
2.扩展名为.p12的证书（可自行百度keytool 生成证书 pkcs12）
3.一个使用acrobat处理过的pdf模板（使用数字签名表单）
二。引入相关maven依赖：
<dependency>
<groupId>com.itextpdfgroupId>
<artifactId>itextpdfartifactId>
<version>5.5.11version>
dependency>
<dependency>
<groupId>com.itextpdfgroupId>
<artifactId>itext-asianartifactId>
<version>5.2.0version>
dependency>
<dependency>
<groupId>org.bouncycastlegroupId>
<artifactId>bcprov-jdk15onartifactId>
<version>1.49version>
dependency>
<dependency>
<groupId>org.bouncycastlegroupId>
<artifactId>bcpkix-jdk15onartifactId>
<version>1.49version>
dependency>
三。编写相关代码，
1.编写签章类，收集签章相关信息
package com.example.itext.utils;
import com.itextpdf.text.pdf.PdfSignatureAppearance;
import com.itextpdf.text.pdf.security.MakeSignature;
import lombok.Data;
import java.security.PrivateKey;
import java.security.cert.Certificate;
@Data
public class SignatureInfo {
private String reason; //理由
private String location;//位置
private String digestAlgorithm;//摘要类型
private String imagePath;//图章路径
private String fieldName;//表单域名称
private Certificate[] chain;//证书链
private PrivateKey pk;//私钥
private int certificationLevel = 0; //批准签章
private PdfSignatureAppearance.RenderingMode renderingMode;//表现形式：仅描述，仅图片，图片和描述，签章者和描述
private MakeSignature.CryptoStandard subfilter;//支持标准，CMS,CADES
}
2.编写工具类，红色字体为完成签章的主体逻辑，以ByteArrayOutputStream充当输出流是为了完成多次签章，期间不会生成临时文件。MakeSignature.signDetached()方法每调用一次，必须重新获取
PdfSignatureAppearance对象，因为分析源码方法可知，该方法调用时，appearance对象的preClosed参数会被置为false。
package com.example.itext.utils;
import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfSignatureAppearance;
import com.itextpdf.text.pdf.PdfStamper;
import com.itextpdf.text.pdf.security.BouncyCastleDigest;
import com.itextpdf.text.pdf.security.DigestAlgorithms;
import com.itextpdf.text.pdf.security.ExternalDigest;
import com.itextpdf.text.pdf.security.ExternalSignature;
import com.itextpdf.text.pdf.security.MakeSignature;
import com.itextpdf.text.pdf.security.PrivateKeySignature;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.KeyStore;
import java.security.PrivateKey;
import java.security.cert.Certificate;
public class ItextUtil {
public static final char[] PASSWORD = "123456".toCharArray();//keystory密码
/**
* 单多次签章通用
* @param src
* @param target
* @param signatureInfos
* @throws GeneralSecurityException
* @throws IOException
* @throws DocumentException
*/
public void sign(String src, String target, SignatureInfo... signatureInfos){
InputStream inputStream = null;
FileOutputStream outputStream = null;
ByteArrayOutputStream result = new ByteArrayOutputStream();
try {
inputStream = new FileInputStream(src);
for (SignatureInfo signatureInfo : signatureInfos) {
ByteArrayOutputStream tempArrayOutputStream = new ByteArrayOutputStream();
PdfReader reader = new PdfReader(inputStream);
//创建签章工具PdfStamper ，最后一个boolean参数是否允许被追加签名
PdfStamper stamper = PdfStamper.createSignature(reader, tempArrayOutputStream, '\0', null, true);
// 获取数字签章属性对象
PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
appearance.setReason(signatureInfo.getReason());
appearance.setLocation(signatureInfo.getLocation());
//设置签名的签名域名称，多次追加签名的时候，签名预名称不能一样，图片大小受表单域大小影响（过小导致压缩）
appearance.setVisibleSignature(signatureInfo.getFieldName());
//读取图章图片
Image image = Image.getInstance(signatureInfo.getImagePath());
appearance.setSignatureGraphic(image);
appearance.setCertificationLevel(signatureInfo.getCertificationLevel());
//设置图章的显示方式，如下选择的是只显示图章（还有其他的模式，可以图章和签名描述一同显示）
appearance.setRenderingMode(signatureInfo.getRenderingMode());
// 摘要算法
ExternalDigest digest = new BouncyCastleDigest();
// 签名算法
ExternalSignature signature = new PrivateKeySignature(signatureInfo.getPk(), signatureInfo.getDigestAlgorithm(), null);
// 调用itext签名方法完成pdf签章
MakeSignature.signDetached(appearance, digest, signature, signatureInfo.getChain(), null, null, null, 0, signatureInfo.getSubfilter());
//定义输入流为生成的输出流内容，以完成多次签章的过程
inputStream = new ByteArrayInputStream(tempArrayOutputStream.toByteArray());
result = tempArrayOutputStream;
}
outputStream = new FileOutputStream(new File(target));
outputStream.write(result.toByteArray());
outputStream.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if(null!=outputStream){
outputStream.close();
}
if(null!=inputStream){
inputStream.close();
}
if(null!=result){
result.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
try {
ItextUtil app = new ItextUtil();
//将证书文件放入指定路径，并读取keystore ，获得私钥和证书链
String pkPath = app.getClass().getResource("/template/zhengshu.p12").getPath();
KeyStore ks = KeyStore.getInstance("PKCS12");
ks.load(new FileInputStream(pkPath), PASSWORD);
String alias = ks.aliases().nextElement();
PrivateKey pk = (PrivateKey) ks.getKey(alias, PASSWORD);
Certificate[] chain = ks.getCertificateChain(alias);
String src = app.getClass().getResource("/template/check.pdf").getPath();
//封装签章信息
SignatureInfo info = new SignatureInfo();
info.setReason("理由");
info.setLocation("位置");
info.setPk(pk);
info.setChain(chain);
info.setCertificationLevel(PdfSignatureAppearance.NOT_CERTIFIED);
info.setDigestAlgorithm(DigestAlgorithms.SHA1);
info.setFieldName("sig1");
info.setImagePath(app.getClass().getResource("/template/yinzhang.png").getPath());
info.setRenderingMode(PdfSignatureAppearance.RenderingMode.GRAPHIC);
SignatureInfo info1 = new SignatureInfo();
info1.setReason("理由1");
info1.setLocation("位置1");
info1.setPk(pk);
info1.setChain(chain);
info1.setCertificationLevel(PdfSignatureAppearance.NOT_CERTIFIED);
info1.setDigestAlgorithm(DigestAlgorithms.SHA1);
info1.setFieldName("sig2");
info1.setImagePath(app.getClass().getResource("/template/yinzhang.png").getPath());
info1.setRenderingMode(PdfSignatureAppearance.RenderingMode.GRAPHIC);
app.sign(src, "D://sign.pdf", info,info1);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
至此，电子签章的代码整理完毕。