使用java代码实现签发服务器通信证书

可以使用Java的KeyStore类来生成和管理证书。以下是一个简单的示例代码：

import java.io.FileOutputStream;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.cert.X509Certificate;
import java.util.Date;

import javax.security.auth.x500.X500Principal;

import sun.security.x509.*;

public class CertificateGenerator {

    public static void main(String[] args) throws Exception {

        // Generate a key pair
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        // Generate a self-signed X.509 certificate
        X500Name issuer = new X500Name("CN=My Company, O=My Organization, L=My City, ST=My State, C=My Country");
        X500Name subject = issuer;
        Date startDate = new Date(System.currentTimeMillis() - 24 * 60 * 60 * 1000); // Yesterday
        Date endDate = new Date(System.currentTimeMillis() + 365 * 24 * 60 * 60 * 1000); // One year from now
        BigInteger serialNumber = new BigInteger(64, new SecureRandom());
        X509CertInfo certInfo = new X509CertInfo();
        certInfo.set(X509CertInfo.VERSION, new CertificateVersion(CertificateVersion.V3));
        certInfo.set(X509CertInfo.SERIAL_NUMBER, new CertificateSerialNumber(serialNumber));
        certInfo.set(X509CertInfo.SUBJECT, new CertificateSubjectName(subject));
        certInfo.set(X509CertInfo.ISSUER, new CertificateIssuerName(issuer));
        certInfo.set(X509CertInfo.VALIDITY, new CertificateValidity(startDate, endDate));
        certInfo.set(X509CertInfo.KEY, new CertificateX509Key(keyPair.getPublic()));
        certInfo.set(X509CertInfo.ALGORITHM_ID, new CertificateAlgorithmId(new AlgorithmId(AlgorithmId.sha256WithRSAEncryption_oid)));
        X509CertImpl cert = new X509CertImpl(certInfo);
        cert.sign(keyPair.getPrivate(), "SHA256withRSA");

        // Save the certificate to a file
        FileOutputStream fos = new FileOutputStream("server.crt");
        fos.write(cert.getEncoded());
        fos.close();

        // Save the private key to a file
        fos = new FileOutputStream("server.key");
        fos.write(keyPair.getPrivate().getEncoded());
        fos.close();

    }

}

这个示例代码生成一个2048位的RSA密钥对，并使用SHA256withRSA签名算法生成一个自签名的X.509证书。证书的有效期为一年，保存在server.crt文件中，私钥保存在server.key文件中。