从X509Certificate对象导出私钥

import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.security.Key;
import java.security.KeyStore;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.cert.CertificateEncodingException;
import java.security.cert.X509Certificate;

public class X509CertificatePrivateKeyExtractor {

    public static void main(String[] args) throws Exception {
        String certificatePath = "path/to/certificate.pem";
        String privateKeyPath = "path/to/privateKey.pem";
        String keyStorePath = "path/to/keystore.jks";
        String keyStorePassword = "yourKeystorePassword";
        String keyAlias = "yourKeyAlias";

        // 读取证书
        X509Certificate certificate = readCertificate(certificatePath);

        // 从证书中提取私钥
        PrivateKey privateKey = extractPrivateKey(certificate);

        // 将私钥保存到文件
        savePrivateKey(privateKey, privateKeyPath);

        // 将证书和私钥导入到KeyStore中
        importCertificateAndPrivateKeyToKeyStore(certificate, privateKey, keyStorePath, keyStorePassword, keyAlias);
    }

    private static X509Certificate readCertificate(String certificatePath) throws IOException, CertificateEncodingException {
        byte[] certificateBytes = Files.readAllBytes(Paths.get(certificatePath));
        return X509Certificate.getInstance(certificateBytes);
    }

    private static PrivateKey extractPrivateKey(X509Certificate certificate) throws NoSuchAlgorithmException {
        Key key = certificate.getPublicKey();
        return (PrivateKey) key;
    }

    private static void savePrivateKey(PrivateKey privateKey, String privateKeyPath) throws IOException {
        try (FileOutputStream fos = new FileOutputStream(privateKeyPath)) {
            fos.write(privateKey.getEncoded());
        }
    }

    private static void importCertificateAndPrivateKeyToKeyStore(X509Certificate certificate, PrivateKey privateKey, String keyStorePath, String keyStorePassword, String keyAlias) throws Exception {
        KeyStore keyStore = KeyStore.getInstance("JKS");

        // 如果KeyStore文件不存在，则创建一个新的空的KeyStore
        if (!Files.exists(Paths.get(keyStorePath))) {
            keyStore.load(null, keyStorePassword.toCharArray());
        } else {
            try (FileInputStream fis = new FileInputStream(keyStorePath)) {
                keyStore.load(fis, keyStorePassword.toCharArray());
            }
        }

        keyStore.setKeyEntry(keyAlias, privateKey, keyStorePassword.toCharArray(), new X509Certificate[]{certificate});

        try (FileOutputStream fos = new FileOutputStream(keyStorePath)) {
            keyStore.store(fos, keyStorePassword.toCharArray());
        }
    }
}