我需要一个java实现sm4加密的代码

以下是Java实现SM4加密的代码，需要使用Bouncy Castle加密库：

import org.bouncycastle.crypto.engines.SM4Engine;
import org.bouncycastle.crypto.modes.CBCBlockCipher;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithIV;
import org.bouncycastle.util.encoders.Hex;

import java.nio.charset.StandardCharsets;
import java.security.Security;

public class SM4Util {

    static {
        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
    }

    /**
     * SM4加密
     *
     * @param plainText 明文
     * @param key       密钥
     * @param iv        IV
     * @return 密文
     */
    public static String encrypt(String plainText, String key, String iv) {
        try {
            byte[] keyBytes = key.getBytes(StandardCharsets.UTF_8);
            byte[] ivBytes = iv.getBytes(StandardCharsets.UTF_8);
            byte[] data = plainText.getBytes(StandardCharsets.UTF_8);

            SM4Engine engine = new SM4Engine();
            CBCBlockCipher cipher = new CBCBlockCipher(engine);

            ParametersWithIV parameterIV = new ParametersWithIV(new KeyParameter(keyBytes), ivBytes);
            cipher.init(true, parameterIV);

            byte[] encrypted = new byte[cipher.getOutputSize(data.length)];
            int len = cipher.processBytes(data, 0, data.length, encrypted, 0);
            cipher.doFinal(encrypted, len);

            return Hex.toHexString(encrypted);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * SM4解密
     *
     * @param cipherText 密文
     * @param key        密钥
     * @param iv         IV
     * @return 明文
     */
    public static String decrypt(String cipherText, String key, String iv) {
        try {
            byte[] keyBytes = key.getBytes(StandardCharsets.UTF_8);
            byte[] ivBytes = iv.getBytes(StandardCharsets.UTF_8);
            byte[] data = Hex.decode(cipherText);

            SM4Engine engine = new SM4Engine();
            CBCBlockCipher cipher = new CBCBlockCipher(engine);

            ParametersWithIV parameterIV = new ParametersWithIV(new KeyParameter(keyBytes), ivBytes);
            cipher.init(false, parameterIV);

            byte[] decrypted = new byte[cipher.getOutputSize(data.length)];
            int len = cipher.processBytes(data, 0, data.length, decrypted, 0);
            cipher.doFinal(decrypted, len);

            return new String(decrypted, StandardCharsets.UTF_8);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

使用示例：

String plainText = "Hello, world!";

String key = "0123456789abcdef0123456789abcdef";
String iv = "0123456789abcdef";

String cipherText = SM4Util.encrypt(plainText, key, iv);
System.out.println("Cipher text: " + cipherText);

String decryptedText = SM4Util.decrypt(cipherText, key, iv);
System.out.println("Decrypted text: " + decryptedText);

注意：SM4算法使用的密钥长度为128位，即16个字节；IV长度为16个字节。在实际应用中，需要使用安全的随机数生成器生成密钥和IV。