<dependency>
  <groupId>org.bouncycastle</groupId>
  <artifactId>bcprov-jdk15to18</artifactId>
  <version>1.69</version>
</dependency>
<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.8.5</version>
</dependency>

package org.demo.utils;

import cn.hutool.crypto.symmetric.SymmetricCrypto; 
import cn.hutool.core.util.StrUtil;

public class SM4Utils {

	//key必須是16字節(jié)，即128位
	final static String key = "testsm4key123456";

	//指明加密算法和秘鑰
	static SymmetricCrypto sm4 = new SymmetricCrypto("SM4/ECB/PKCS5Padding", key.getBytes());

	/**
	 * 加密為16進(jìn)制，也可以加密成base64/字節(jié)數(shù)組
	 *
	 * @param plaintext
	 * @return
	 */
	public static String encryptSm4(String plaintext) {
		if (StrUtil.isBlank(plaintext)) {
			return "";
		}
		return sm4.encryptHex(plaintext);
	}

	/**
	 * 解密
	 *
	 * @param ciphertext
	 * @return
	 */
	public static String decryptSm4(String ciphertext) {
		if (StrUtil.isBlank(ciphertext)) {
			return "";
		}
		return sm4.decryptStr(ciphertext);
	}
}

    public static void main(String[] args) {
        String str =  SM4Utils.encryptSm4("測試加密");
        System.out.println("加密后的字符串為"+str);
        System.out.println("解密后的字符串為"+SM4Utils.decryptSm4(str));
    }