PKCS10生成证书csr

public static String genCSR(String subject, String alg,String provider)
            throws InvalidKeyException, NoSuchAlgorithmException,
            NoSuchProviderException, SignatureException, OperatorCreationException {
        String signalg="";
        int alglength=0;
        String keyAlg="";
        if(alg.toUpperCase().equals("RSA1024")){
            signalg="SHA1WithRSA";
            alglength=1024;
            keyAlg="RSA";
        }else if(alg.toUpperCase().equals("RSA2048")){
            signalg="SHA1WithRSA";
            alglength=2048;
            keyAlg="RSA";
        }else if(alg.toUpperCase().equals("SM2")){
            signalg="SM3withSM2";
            alglength=256;
            keyAlg="SM2";
        }
        KeyPairGenerator keyGen = KeyPairGenerator.getInstance(keyAlg);
        keyGen.initialize(alglength);
        KeyPair kp = keyGen.generateKeyPair();
        PKCS10CertificationRequestBuilder builder = new PKCS10CertificationRequestBuilder(new X500Name(subject),SubjectPublicKeyInfo.getInstance(kp.getPublic().getEncoded()));
        JcaContentSignerBuilder jcaContentSignerBuilder = new JcaContentSignerBuilder(signalg);
        jcaContentSignerBuilder.setProvider(provider);
        ContentSigner contentSigner = jcaContentSignerBuilder.build(kp.getPrivate());
        builder.build(contentSigner);
        return builder.toString();
    }