1 加密方法：

1.1 java自带jar工具MessageDigest实现

java.security.MessageDigest

public class MD5Utils {
    public static String stringToMD5(String plainText) {
        byte[] secretBytes = null;
        try {
            secretBytes = MessageDigest.getInstance("md5").digest(
                    plainText.getBytes());
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException("没有这个md5算法！");
        }
        String md5code = new BigInteger(1, secretBytes).toString(16);
        for (int i = 0; i < 32 - md5code.length(); i++) {
            md5code = "0" + md5code;
        }
        return md5code;
    }

}

1.2 spring自带的工具DigestUtils实现

org.springframework.util.DigestUtils

DigestUtils.md5DigestAsHex("1234".getBytes())

2 使用方法：

2.1 使用MessageDigest

@Test
public void testMd5() throws NoSuchAlgorithmException{
    MessageDigest md = MessageDigest.getInstance("MD5");
    // java自带工具包MessageDigest  
    String resultString = MD5Utils.md5("123456");
    System.out.println(resultString);
    // e10adc3949ba59abbe56e057f20f883e
    String resultString1 = MD5Utils.md5("1234");
    System.out.println(resultString1);
    //81dc9bdb52d04dc20036dbd8313ed055

    // spring自带工具包DigestUtils
    System.out.println(DigestUtils.md5DigestAsHex("1234".getBytes()));
    // 81dc9bdb52d04dc20036dbd8313ed055
}

2.2 使用DigestUtils

@SpringBootTest
class ServerApplicationTests {

    @Test
    void testMd5() {
        String hashpw = DigestUtils.md5Hex("123456".getBytes(StandardCharsets.UTF_8));
        System.out.println(hashpw);
    }