java pdf 签名 修改,使用Java中的自定义数字签名来签名PDF

可以使用Java中的Bouncy Castle库来实现数字签名和PDF文件的签名。下面是一个简单的示例代码，演示如何使用Bouncy Castle库来实现数字签名和对PDF文件进行签名：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.KeyStore;
import java.security.PrivateKey;
import java.security.Security;
import java.security.cert.Certificate;

import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.cms.CMSSignedData;
import org.bouncycastle.cms.CMSProcessableByteArray;
import org.bouncycastle.cms.CMSSignedDataGenerator;
import org.bouncycastle.cms.jcajce.JcaSignerInfoGeneratorBuilder;
import org.bouncycastle.operator.jcajce.JcaContentSignerBuilder;

public class PDFSigner {

    // 指定证书库文件名
    private static final String KEYSTORE_FILE = "keystore.jks";
    // 指定证书库密码
    private static final String KEYSTORE_PASSWORD = "password";
    // 指定证书别名
    private static final String KEY_ALIAS = "mykey";
    // 指定证书密码
    private static final String KEY_PASSWORD = "password";

    public static void main(String[] args) throws Exception {
        // 添加Bouncy Castle安全提供程序
        Security.addProvider(new BouncyCastleProvider());

        // 读取证书库
        KeyStore keystore = KeyStore.getInstance("JKS");
        keystore.load(new FileInputStream(KEYSTORE_FILE), KEYSTORE_PASSWORD.toCharArray());

        // 获取私钥和证书链
        PrivateKey privateKey = (PrivateKey) keystore.getKey(KEY_ALIAS, KEY_PASSWORD.toCharArray());
        Certificate[] certChain = keystore.getCertificateChain(KEY_ALIAS);

        // 读取PDF文件内容
        byte[] pdfContent = readPdfFile("input.pdf");

        // 生成数字签名
        CMSSignedDataGenerator generator = new CMSSignedDataGenerator();
        JcaContentSignerBuilder builder = new JcaContentSignerBuilder("SHA256withRSA");
        builder.setProvider("BC");
        generator.addSignerInfoGenerator(new JcaSignerInfoGeneratorBuilder(
                new JcaDigestCalculatorProviderBuilder().setProvider("BC").build())
                .build(builder.build(privateKey), new X509CertificateHolder(certChain[0].getEncoded())));
        generator.addCertificates(new JcaCertStore(Arrays.asList(certChain)));
        CMSSignedData signedData = generator.generate(new CMSProcessableByteArray(pdfContent), true);

        // 将数字签名添加到PDF文件中
        byte[] signedContent = signedData.getEncoded();
        writePdfFile("output.pdf", signedContent);
    }

    private static byte[] readPdfFile(String filename) throws Exception {
        FileInputStream fis = new FileInputStream(filename);
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len;
        while ((len = fis.read(buffer)) != -1) {
            bos.write(buffer, 0, len);
        }
        fis.close();
        return bos.toByteArray();
    }

    private static void writePdfFile(String filename, byte[] content) throws Exception {
        FileOutputStream fos = new FileOutputStream(filename);
        fos.write(content);
        fos.close();
    }

}

以上示例代码中，首先读取证书库文件，获取私钥和证书链。然后读取PDF文件内容，使用Bouncy Castle库生成数字签名。最后将数字签名添加到PDF文件中。在实际使用过程中，需要替换掉示例代码中的文件名、密码和证书别名等信息，以及使用实际的证书库文件和PDF文件。