SpringBoot中实现多线程分片下载

@GetMapping("/download")
public ResponseEntity<InputStreamResource> downloadFile(
    @RequestHeader(value = "Range", required = false) String rangeHeader,
    HttpServletRequest request) throws IOException {
    
    // 1. 获取文件信息
    File file = new File("/path/to/largefile.zip");
    long fileSize = file.length();
    
    // 2. 解析Range头（支持多线程分片）
    long start = 0, end = fileSize - 1;
    if (rangeHeader != null) {
        String[] ranges = rangeHeader.replace("bytes=", "").split("-");
        start = Long.parseLong(ranges[0]);
        if (ranges.length > 1) {
            end = Long.parseLong(ranges[1]);
        }
    }
    
    // 3. 校验范围合法性
    if (start >= fileSize || end >= fileSize || start > end) {
        return ResponseEntity.status(HttpStatus.REQUESTED_RANGE_NOT_SATISFIABLE)
                .header("Content-Range", "bytes */" + fileSize)
                .build();
    }
    
    // 4. 设置响应头
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
    headers.setContentLength(end - start + 1);
    headers.setHeader("Content-Range", "bytes " + start + "-" + end + "/" + fileSize);
    headers.setHeader("Accept-Ranges", "bytes");
    
    // 5. 返回分片数据流
    try (InputStream is = new FileInputStream(file);
         InputStreamResource resource = new InputStreamResource(is)) {
        is.skip(start);
        return new ResponseEntity<>(resource, headers, HttpStatus.PARTIAL_CONTENT);
    }
}

// 分片下载配置
int THREAD_COUNT = 4; // 线程数
long fileSize = getFileSize(); // 通过HEAD请求获取总大小
long chunkSize = fileSize / THREAD_COUNT;

// 创建线程池
ExecutorService executor = Executors.newFixedThreadPool(THREAD_COUNT);
CountDownLatch latch = new CountDownLatch(THREAD_COUNT);

for (int i = 0; i < THREAD_COUNT; i++) {
    long start = i * chunkSize;
    long end = (i == THREAD_COUNT - 1) ? fileSize - 1 : start + chunkSize - 1;
    
    executor.submit(() -> {
        try {
            // 发送带Range头的请求
            HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
            conn.setRequestProperty("Range", "bytes=" + start + "-" + end);
            
            try (InputStream is = conn.getInputStream();
                 RandomAccessFile raf = new RandomAccessFile("temp.part", "rw")) {
                raf.seek(start); // 定位写入位置
                byte[] buffer = new byte[8192];
                int len;
                while ((len = is.read(buffer)) != -1) {
                    raf.write(buffer, 0, len);
                }
            }
        } catch (IOException e) {
            // 处理重试逻辑
        } finally {
            latch.countDown();
        }
    });
}

// 等待所有线程完成并合并文件
latch.await();
mergeTempFiles("temp.part", "final.file");

// 合并分片文件（按顺序追加）
public static void mergeFiles(List<File> chunkFiles, File targetFile) {
    try (FileOutputStream fos = new FileOutputStream(targetFile)) {
        for (File chunk : chunkFiles) {
            try (FileInputStream fis = new FileInputStream(chunk)) {
                IOUtils.copy(fis, fos);
            }
            chunk.delete(); // 删除临时分片
        }
    } catch (IOException e) {
        throw new RuntimeException("合并失败", e);
    }
}

// 计算文件MD5
public static String calculateMd5(File file) throws IOException {
    try (FileInputStream fis = new FileInputStream(file)) {
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] buffer = new byte[8192];
        int len;
        while ((len = fis.read(buffer)) != -1) {
            md.update(buffer, 0, len);
        }
        return Hex.encodeHexString(md.digest());
    }
}

// 动态线程池（根据CPU核心数调整）
int corePoolSize = Runtime.getRuntime().availableProcessors() * 2;
ExecutorService executor = new ThreadPoolExecutor(
    corePoolSize, 
    corePoolSize * 2,
    60L, TimeUnit.SECONDS,
    new LinkedBlockingDeque<>(1000)
);

// 分片写入优化示例
FileChannel targetChannel = new FileOutputStream("output.zip").getChannel();
for (File chunk : chunks) {
    FileChannel sourceChannel = new FileInputStream(chunk).getChannel();
    sourceChannel.transferTo(0, sourceChannel.size(), targetChannel);
    sourceChannel.close();
}

graph TD
A[获取文件总大小] --> B[计算分片范围]
B --> C[创建线程池]
C --> D[启动分片下载线程]
D --> E{所有线程完成?}
E -->|是| F[合并分片文件]
E -->|否| D
F --> G[校验文件完整性]

# 使用wrk模拟多线程下载
wrk -t4 -c100 -d60s http://localhost:8080/download