我在我的项目中使用这个库来下载文件，它工作得很好。现在我希望我下载的文件和视频必须加密。这是我经过一些研究后设法编写的代码。但它给出了一个下载错误。

public static class MyStorageResolver extends DefaultStorageResolver {
        String ALGORITHM = "Blowfish";
        String MODE = "Blowfish/CBC/PKCS5Padding";
        String IV = "!a3edr45";
        String KEY = "xxxxxxxx";
        Cipher cipher;

        public MyStorageResolver(Context context) {
            super(context, FetchCoreUtils.getFileTempDir(context));
        }

        @NotNull
        @Override

        public OutputResourceWrapper getRequestOutputResourceWrapper(@NotNull Downloader.ServerRequest request) {
            try {
                Key secretKey = new SecretKeySpec(KEY.getBytes(), ALGORITHM);
                cipher = Cipher.getInstance(MODE);
                cipher.init(Cipher.ENCRYPT_MODE, secretKey, new IvParameterSpec(IV.getBytes()));

                return new OutputResourceWrapper() {
                    RandomAccessFile randomAccessFile = new RandomAccessFile(request.getFile(), "rw");

                    @Override
                    public void write(@NotNull byte[] byteArray, int offSet, int length) throws IOException {
                        randomAccessFile.write(cipher.update(byteArray, offSet, length), offSet, length);
                        Log.d("download", "raf writing");
                    }

                    @Override
                    public void setWriteOffset(long offset) throws IOException {
                        int AES_BLOCK_SIZE = 16;
                        int skip = (int) (offset % AES_BLOCK_SIZE);
                        long blockOffset = offset - skip;
                        long numberOfBlocks = blockOffset / AES_BLOCK_SIZE;

                        BigInteger ivForOffsetAsBigInteger = new BigInteger(1, IV.getBytes()).add(BigInteger.valueOf(numberOfBlocks));
                        byte[] ivForOffsetByteArray = ivForOffsetAsBigInteger.toByteArray();
                        IvParameterSpec computedIvParameterSpecForOffset;
                        if (ivForOffsetByteArray.length < AES_BLOCK_SIZE) {
                            byte[] resizedIvForOffsetByteArray = BigInteger.valueOf(AES_BLOCK_SIZE).toByteArray();
                            System.arraycopy(ivForOffsetByteArray, 0, resizedIvForOffsetByteArray, AES_BLOCK_SIZE - ivForOffsetByteArray.length, ivForOffsetByteArray.length);
                            computedIvParameterSpecForOffset = new IvParameterSpec(resizedIvForOffsetByteArray);
                        } else {
                            computedIvParameterSpecForOffset = new IvParameterSpec(ivForOffsetByteArray, ivForOffsetByteArray.length - AES_BLOCK_SIZE, AES_BLOCK_SIZE);
                        }
                        try {
                            cipher.init(Cipher.ENCRYPT_MODE, secretKey, computedIvParameterSpecForOffset);
                        } catch (InvalidAlgorithmParameterException | InvalidKeyException e) {
                            e.printStackTrace();
                        }
                        byte[] skipBuffer = BigInteger.valueOf(skip).toByteArray();
                        try {
                            cipher.update(skipBuffer, 0, skip, skipBuffer);
                        } catch (ShortBufferException e) {
                            e.printStackTrace();
                        }
                        randomAccessFile.seek(offset);

                        Log.d("download", "raf seeked");

                    }

                    @Override
                    public void flush() {
                    }

                    @Override
                    public void close() throws IOException {
                        randomAccessFile.close();
                    }
                };
            } catch (FileNotFoundException | NoSuchAlgorithmException | InvalidKeyException | InvalidAlgorithmParameterException | NoSuchPaddingException e) {
                Log.d("download", "raf error");

                e.printStackTrace();
            }
            return super.getRequestOutputResourceWrapper(request);
        }

    }

我是这样的

FetchConfiguration fetchConfiguration = new FetchConfiguration.Builder(this)
                .setDownloadConcurrentLimit(2)
                .enableRetryOnNetworkGain(true)
//                .setNamespace("TdeskDownloader")
                .enableFileExistChecks(true)
                .setProgressReportingInterval(500)
                .setAutoRetryMaxAttempts(3)
                .setNotificationManager(new DefaultFetchNotificationManager(this) {

                    @Override
                    public void updateNotification(@NotNull NotificationCompat.Builder notificationBuilder, @NotNull DownloadNotification downloadNotification, @NotNull Context context) {
                        Intent intent = new Intent(getBaseContext(), DownloadsActivity.class);
                        PendingIntent pendingIntent = PendingIntent.getActivity(getBaseContext(), 1, intent, PendingIntent.FLAG_UPDATE_CURRENT);

                        notificationBuilder
                                .setOnlyAlertOnce(true)
                                .setColorized(true)
                                .setNotificationSilent()
                                .setContentIntent(pendingIntent)
                                .setAutoCancel(true)
                                .setColor(getResources().getColor(R.color.colorAccent))
                                .setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher_round))
                                .setBadgeIconType(NotificationCompat.BADGE_ICON_SMALL);

                        super.updateNotification(notificationBuilder, downloadNotification, context);
                    }

                    @NotNull
                    @Override
                    public Fetch getFetchInstanceForNamespace(@NotNull String namespace) {
                        return fetch;
                    }

                    @Override
                    public boolean shouldCancelNotification(@NotNull DownloadNotification downloadNotification) {
                        return downloadNotification.getStatus() == Status.CANCELLED;
                    }
                })
                .setHttpDownloader(new HttpUrlConnectionDownloader(Downloader.FileDownloaderType.PARALLEL))
                .setStorageResolver(new MyStorageResolver(this.getApplicationContext()))
                .build();
        Fetch.Impl.setDefaultInstanceConfiguration(fetchConfiguration);

        fetch = Fetch.Impl.getDefaultInstance();

这是错误日志：

2021-07-10 04:19:15.724 E/LibGlobalFetchLib: FileDownloader download:DownloadInfo(id=-1757988576, namespace='LibGlobalFetchLib', url='https://file-examples-com.github.io/uploads/2017/10/file-example_PDF_500_kB.pdf', file='/storage/emulated/0/Download/tdesk/file-example_PDF_500_kB.pdf', group=0, priority=HIGH, headers={}, downloaded=0, total=469513, status=DOWNLOADING, error=NONE, networkType=ALL, created=1625870930995, tag=null, enqueueAction=UPDATE_ACCORDINGLY, identifier=0, downloadOnEnqueue=true, extras={"mime":"application\/pdf"}, autoRetryMaxAttempts=0, autoRetryAttempts=3, etaInMilliSeconds=-1, downloadedBytesPerSecond=-1)
java.lang.ArrayIndexOutOfBoundsException: src.length=8 srcPos=0 dst.length=1 dstPos=8 length=8
    at java.lang.System.arraycopy(Native Method)
    at com.toppersdesk.app.commonUtility$MyStorageResolver$1.setWriteOffset(commonUtility.java:366)
    at com.tonyodev.fetch2.downloader.ParallelFileDownloaderImpl.downloadSliceFiles(ParallelFileDownloaderImpl.kt:416)
    at com.tonyodev.fetch2.downloader.ParallelFileDownloaderImpl.run(ParallelFileDownloaderImpl.kt:149)
    at com.tonyodev.fetch2.downloader.DownloadManagerImpl$start$$inlined$synchronized$lambda$1.run(DownloadManagerImpl.kt:103)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
    at java.lang.Thread.run(Thread.java:764)

也许我犯了一些与课堂有关的基本错误。有人能帮我指出我在代码中犯的错误吗？
编辑：我将按照本期中的示例实现简历支持的密码加密。我从未使用过这个类，所以我不知道示例代码中提供的逻辑到底有什么问题。