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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.itextpdf</groupId><artifactId>itextpdf</artifactId><version>5.5.11</version></dependency><dependency><groupId>com.itextpdf</groupId><artifactId>itext-asian</artifactId><version>5.2.0</version></dependency><dependency><groupId>org.bouncycastle</groupId><artifactId>bcprov-jdk15on</artifactId><version>1.49</version></dependency><dependency><groupId>org.bouncycastle</groupId><artifactId>bcpkix-jdk15on</artifactId><version>1.49</version></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。