public AliyunOssSignatureView genSignature() throws Exception {

        // 步驟1：創建policy。
        ObjectMapper mapper = new ObjectMapper();

        Map<String, Object> policy = new HashMap<>();
        policy.put("expiration", formatISODateTime());

        List<Object> conditions = new ArrayList<>();

        Map<String, String> bucketCondition = new HashMap<>();
        bucketCondition.put("bucket", bucketName);
        conditions.add(bucketCondition);

        Map<String, String> signatureVersionCondition = new HashMap<>();
        signatureVersionCondition.put("x-oss-signature-version", "OSS4-HMAC-SHA256");
        conditions.add(signatureVersionCondition);

        Map<String, String> credentialCondition = new HashMap<>();
        credentialCondition.put("x-oss-credential", accessKeyId + "/" + formatISODate() +  "/" + region + "/oss/aliyun_v4_request"); // 替換為實際的 access key id
        conditions.add(credentialCondition);

        Map<String, String> dateCondition = new HashMap<>();
        dateCondition.put("x-oss-date", formateDateTimeZ());
        conditions.add(dateCondition);

        conditions.add(Arrays.asList("content-length-range", 1L, 1024L*1024*1024*5));
        conditions.add(Arrays.asList("eq", "$success_action_status", "201"));
//        conditions.add(Arrays.asList("starts-with", "$key", "user/eric/"));
//        conditions.add(Arrays.asList("in", "$content-type", Arrays.asList("image/jpg", "image/png")));
//        conditions.add(Arrays.asList("not-in", "$cache-control", Arrays.asList("no-cache")));

        policy.put("conditions", conditions);

        String jsonPolicy = mapper.writeValueAsString(policy);
        // 步驟2：構造待簽名字符串（StringToSign）。
        String stringToSign = new String(Base64.encodeBase64(jsonPolicy.getBytes()));


        // 步驟3：計算SigningKey。
        byte[] dateKey = hmacsha256(("aliyun_v4" + accessKeySecret).getBytes(), formatISODate());
        byte[] dateRegionKey = hmacsha256(dateKey, region);
        byte[] dateRegionServiceKey = hmacsha256(dateRegionKey, "oss");
        byte[] signingKey = hmacsha256(dateRegionServiceKey, "aliyun_v4_request");

        // 步驟4：計算Signature。
        byte[] result = hmacsha256(signingKey, stringToSign);
        String signature = BinaryUtil.toHex(result);
        log.info("policy:{}, base64 policy:{}, signature:{}", jsonPolicy, stringToSign, signature);
        return new AliyunOssSignatureView(stringToSign, signature);
    }

 public static byte[] hmacsha256(byte[] key, String data) {
        try {
            // 初始化HMAC密鑰規格，指定算法為HMAC-SHA256并使用提供的密鑰。
            SecretKeySpec secretKeySpec = new SecretKeySpec(key, "HmacSHA256");

            // 獲取Mac實例，并通過getInstance方法指定使用HMAC-SHA256算法。
            Mac mac = Mac.getInstance("HmacSHA256");
            // 使用密鑰初始化Mac對象。
            mac.init(secretKeySpec);

            // 執行HMAC計算，通過doFinal方法接收需要計算的數據并返回計算結果的數組。
            byte[] hmacBytes = mac.doFinal(data.getBytes());

            return hmacBytes;
        } catch (Exception e) {
            throw new RuntimeException("Failed to calculate HMAC-SHA256", e);
        }
    }

    /**
     * 獲取ISO格式時間
     * 2024-12-03T13:00:00Z
     * @return current time iso format
     */
    public static String formatISODateTime() {
        ZonedDateTime utcTime = ZonedDateTime.now();
        utcTime = utcTime.plusHours(1);
        return utcTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"));
    }

    public static String formatISODate() {

        LocalDate utcDate = LocalDate.now(ZoneOffset.UTC);
        return utcDate.format(DateTimeFormatter.ofPattern("yyyyMMdd"));
    }

    public static String formateDateTimeZ() {
        ZonedDateTime utcTime = ZonedDateTime.now(ZoneOffset.UTC);
        return utcTime.format(DateTimeFormatter.ofPattern("yyyyMMdd'T'HHmmss'Z'"));
    }