如何使用Java语言实现文件分片上传和断点续传功能？

// 创建RandomAccessFile对象
RandomAccessFile raf = new RandomAccessFile(file, "r");

// 计算数据块大小
long blockSize = file.length() / numThreads;
if (file.length() % numThreads != 0) {
    blockSize++;
}

// 切割文件并保存到磁盘
for (int i = 0; i < numThreads; i++) {
    long start = i * blockSize;
    long end = Math.min(start + blockSize, file.length());
    byte[] buff = new byte[(int) (end - start)];

    raf.seek(start);
    raf.read(buff);

    String path = savePath + File.separator + i + ".part";
    try (FileOutputStream fos = new FileOutputStream(path)) {
        fos.write(buff);
    }
}

// 创建线程池
ExecutorService executor = Executors.newFixedThreadPool(numThreads);

// 启动上传线程
for (int i = 0; i < numThreads; i++) {
    String path = savePath + File.separator + i + ".part";
    File file = new File(path);

    if (!file.exists()) {
        continue;
    }

    // 获取文件上传状态
    UploadStatus status = getStatus(i);

    // 跳过已上传的数据块
    if (status.getTotal() == file.length()) {
        continue;
    }

    // 创建上传任务
    UploadTask task = new UploadTask(i, url, file, status, this);

    // 提交任务到线程池
    executor.execute(task);
}

// 关闭线程池
executor.shutdown();

// 初始化数据库
public void initDatabase() {
    // 创建表
    String sql = "CREATE TABLE IF NOT EXISTS upload (" +
            "id INT PRIMARY KEY, " +
            "total LONG, " +
            "uploaded LONG)";
    jdbcTemplate.execute(sql);

    // 初始化数据
    for (int i = 0; i < numThreads; i++) {
        String sql2 = "INSERT INTO upload (id, total, uploaded) VALUES (?, ?, ?)";
        jdbcTemplate.update(sql2, i, 0L, 0L);
    }
}

// 获取上传状态
public UploadStatus getStatus(int id) {
    String sql = "SELECT * FROM upload WHERE id = ?";
    Map<String, Object> map = jdbcTemplate.queryForMap(sql, id);

    long total = (long) map.get("total");
    long uploaded = (long) map.get("uploaded");

    return new UploadStatus(total, uploaded);
}

// 更新上传状态
public void updateStatus(int id, long uploaded) {
    String sql = "UPDATE upload SET uploaded = ? WHERE id = ?";
    jdbcTemplate.update(sql, uploaded, id);
}

// 上传数据块
private void uploadPart(int id, File file, long start, long end) throws IOException {
    int retry = 0;
    while (true) {
        try {
            // 创建HTTP连接
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(10000);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/octet-stream");
            conn.setRequestProperty("Range", "bytes=" + start + "-" + end);

            // 上传数据
            try (RandomAccessFile raf = new RandomAccessFile(file, "r")) {
                byte[] buffer = new byte[1024];
                int len;
                long progress = start;
                raf.seek(start);
                InputStream input = conn.getInputStream();
                OutputStream output = conn.getOutputStream();
                while ((len = raf.read(buffer)) != -1) {
                    output.write(buffer, 0, len);
                    progress += len;
                    updateStatus(id, progress);
                }

                // 更新上传状态
                updateStatus(id, end + 1);

                // 关闭流
                input.close();
                output.close();
            }

            // 关闭连接
            conn.disconnect();

            break;
        } catch (IOException ex) {
            retry++;
            if (retry > MAX_RETRY) {
                throw ex;
            }
        }
    }
}