架构师训练营十一周作业

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Optional;
public class UserPasswordService {
    private static final char[] HEX_DIGITS = {
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
    };
    private Optional<String> encryptByMD5(String password, String salt) {
        if(password == null || password.isEmpty()) throw new IllegalArgumentException("password cannot be null");
        if(salt == null || salt.isEmpty()) throw new IllegalArgumentException("salt cannot be null");
        String original = password + salt;
        byte[] originalBytes = original.getBytes();
        try {
            MessageDigest md5 = MessageDigest.getInstance("MD5");
            md5.update(originalBytes);
            // 获得密文
            byte[] md5Bytes = md5.digest();
            // 把密文转换成十六进制的字符串形式
            int len = md5Bytes.length;
            char[] str = new char[len * 2];
            int k = 0;
            for (byte byte0 : md5Bytes) {
                str[k++] = HEX_DIGITS[byte0 >>> 4 & 0xf];
                str[k++] = HEX_DIGITS[byte0 & 0xf];
            }
            return Optional.of(new String(str));
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
            return Optional.empty();
        }
    }
    public boolean checkPW(String userId, String password, String encryptedPassword) {
        //use user id as salt
        Optional<String> optional = this.encryptByMD5(password, userId);
        return optional.map(s -> s.equals(encryptedPassword)).orElse(false);
    }
}