springboot下载接口限速功能实现

客户端发起请求
     ↓
download(...) 方法被调用
     ↓
从 Redis 增加并发数 DOWNLOAD_CONCURRENT_KEY
     ↓
根据并发数计算限速值（getDownloadSpeedLimit）
     ↓
调用 limitReadFile(...) 开始下载文件
     ↓
limitReadFile(...) 内部调用 FileUtil.limitDownloadSpeed(...)
     ↓
读取文件内容 → 分段写入输出流 → 控制每秒发送的数据量
     ↓
下载完成或客户端断开连接
     ↓
finally 中减少 Redis 的并发数

// 增加并发计数器
Long currentConcurrent = redisTemplate.opsForValue().increment(DOWNLOAD_CONCURRENT_KEY);
// 更新过期时间
redisTemplate.expire(DOWNLOAD_CONCURRENT_KEY, EXPIRE_TIME_IN_SECONDS, TimeUnit.SECONDS);
// 计算限速值
int speedLimit = getDownloadSpeedLimit(currentConcurrent.intValue());

private int getDownloadSpeedLimit(int concurrentCount) {
    int totalBandwidth = 1024 * 1024 * 5; // 总带宽 5MB/s
    int perUserSpeed = totalBandwidth / Math.max(1, concurrentCount);
    return Math.max(perUserSpeed, 1024 * 50); // 最低限速 50KB/s
}

public static void limitDownloadSpeed(InputStream in, OutputStream out, int bytesPerSecond) throws IOException {
    byte[] buffer = new byte[BUFFER_SIZE]; // 默认是 1024 字节
    int bytesRead;
    long bytesSent = 0;
    long startTime = System.currentTimeMillis();
    while ((bytesRead = in.read(buffer)) != -1) {
        out.write(buffer, 0, bytesRead);
        bytesSent += bytesRead;
        if (bytesSent >= bytesPerSecond) {
            long elapsedTime = System.currentTimeMillis() - startTime;
            if (elapsedTime < 1000) {
                Thread.sleep(1000 - elapsedTime);
            }
            bytesSent = 0;
            startTime = System.currentTimeMillis();
        }
    }
}