数字证书java代码实现

数字证书是一种用于验证身份和加密通信安全工具。在Java中，可以使用Java的密钥库（KeyStore）和相关类来实现数字证书的功能。下面是一个简单的示例代码，演示了如何生成数字证书和使用数字证书进行加密和解密：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.*;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import javax.crypto.Cipher;

public class DigitalCertificateExample {
    public static void main(String[] args) throws Exception {
        // 生成数字证书
        generateCertificate();

        // 使用数字证书进行加密和解密
        encryptAndDecrypt();
    }

    public static void generateCertificate() throws Exception {
        // 生成密钥对
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        // 创建自签名证书
        X509Certificate cert = generateSelfSignedCertificate(keyPair);

        // 将证书保存到文件
        FileOutputStream fos = new FileOutputStream("certificate.cer");
        fos.write(cert.getEncoded());
        fos.close();
    }

    public static X509Certificate generateSelfSignedCertificate(KeyPair keyPair) throws Exception {
        // 创建证书生成工厂
        CertificateFactory cf = CertificateFactory.getInstance("X.509");

        // 创建证书生成器
        X509V3CertificateGenerator certGen = new X509V3CertificateGenerator();
        certGen.setSerialNumber(BigInteger.valueOf(System.currentTimeMillis()));
        certGen.setIssuerDN(new X500Principal("CN=Self Signed Certificate"));
        certGen.setNotBefore(new Date(System.currentTimeMillis() - 1000L * 60 * 60 * 24));        certGen.setNotAfter(new Date(System.currentTimeMillis() + 1000L * 60 * 60 * 24 * 365));
        certGen.setSubjectDN(new X500Principal("CN=Self Signed Certificate"));
        certGen.setPublicKey(keyPair.getPublic());
        certGen.setSignatureAlgorithm("SHA256WithRSA");

        // 生成证书
        return certGen.generate(keyPair.getPrivate(), "BC");
    }

    public static void encryptAndDecrypt() throws Exception {
        // 加载数字证书
        FileInputStream fis = new FileInputStream("certificate.cer");
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        Certificate cert = cf.generateCertificate(fis);
        PublicKey publicKey = cert.getPublicKey();

        // 加密数据
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] encryptedData = cipher.doFinal("Hello, World!".getBytes());

        // 解密数据
        PrivateKey privateKey = keyPair.getPrivate();
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] decryptedData = cipher.doFinal(encryptedData);

        System.out.println("Decrypted Data: " + new String(decryptedData));
    }
}

请注意，上述代码仅为示例，实际使用时可能需要根据具体需求进行修改和完善。