import org.bouncycastle.util.io.pem.PemObjectGenerator; //导入依赖的package包/类
/**
 * Creates and returns the content of a new singing request for the specified certificate. Signing
 * requests are required by Certificate Authorities as part of their signing process. The signing request
 * contains information about the certificate issuer, subject DN, subject alternative names and public key.
 * Private keys are not included. After the Certificate Authority verified and signed the certificate a new
 * certificate is going to be returned.
 *
 * @param cert the certificate to create a signing request.
 * @param privKey the private key of the certificate.
 * @return the content of a new singing request for the specified certificate.
 */
public static String createSigningRequest(X509Certificate cert, PrivateKey privKey) throws OperatorCreationException, IOException {

    JcaPKCS10CertificationRequestBuilder csrBuilder = new JcaPKCS10CertificationRequestBuilder( //
            cert.getSubjectX500Principal(), //
            cert.getPublicKey() //
            );

    String signatureAlgorithm = "SHA256WITH" + cert.getPublicKey().getAlgorithm();

    ContentSigner signer = new JcaContentSignerBuilder(signatureAlgorithm).build(privKey);
    PKCS10CertificationRequest csr = csrBuilder.build(signer);

    StringWriter string = new StringWriter();
    PemWriter pemWriter = new PemWriter(string);

    PemObjectGenerator objGen = new MiscPEMGenerator(csr);
    pemWriter.writeObject(objGen);
    pemWriter.close();

    return string.toString();
}
 

import org.bouncycastle.util.io.pem.PemObjectGenerator; //导入依赖的package包/类
public void writeObject(
    PemObjectGenerator obj)
    throws IOException
{
    super.writeObject(obj);
}