ASP.NET实现文件下载的功能

转载自：https://www.50bit.cn/News/Index/1099.html

　　文件下载是很多网站中含有的常用功能，在ASP.NET中可以使用FileStream类、HttpRequest对象、HttpResponse对象相互结合，实现输出硬盘文件的功能。该方法支持大文件、续传、速度限制、资源占用小。

　　FileStream类：MSDN上的解释为，FileStrem类对文件系统上的文件进行读取、写入、打开和关闭操作，并对其他与文件相关的操作系统句柄进行操作，如管道、标准输入和标准输出。读写操作可以指定为同步或异步操作。FileStream 对输入输出进行缓冲，从而提高性能。

　　Response对象：ASP.NET网站中对外输出信息流的基础对象实体。

下面是封装后的代码，如果你不想用封装代码，可以把封装函数取消，相应能数换成实体值就可以。

       /// <summary>
        ///  输出硬盘文件，提供下载 支持大文件、续传、速度限制、资源占用小
        /// </summary>
        /// <param name="_Request">Page.Request对象</param>
        /// <param name="_Response">Page.Response对象</param>
        /// <param name="_fileName">下载文件名</param>
        /// <param name="_fullPath">带文件名下载路径</param>
        /// <param name="_speed">每秒允许下载的字节数</param>
        /// <returns>返回是否成功</returns>
        public static bool ResponseFile(HttpRequest _Request, HttpResponse _Response, string _fileName, string _fullPath, long _speed)
        {
            try
            {
                FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                BinaryReader br = new BinaryReader(myFile);
                try
                {
                    _Response.AddHeader("Accept-Ranges", "bytes");
                    _Response.Buffer = false;
                    long fileLength = myFile.Length;
                    long startBytes = 0;

                    int pack = 10240; //10K bytes
                    //int sleep = 200;   //每秒5次   即5*10K bytes每秒
                    int sleep = (int)Math.Floor((double)(1000 * pack / _speed)) + 1;
                    if (_Request.Headers["Range"] != null)
                    {
                        _Response.StatusCode = 206;
                        string[] range = _Request.Headers["Range"].Split(new char[] { '=', '-' });
                        startBytes = Convert.ToInt64(range[1]);
                    }
                    _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                    if (startBytes != 0)
                    {
                        _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
                    }
                    _Response.AddHeader("Connection", "Keep-Alive");
                    _Response.ContentType = "application/octet-stream";
                    _Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(_fileName, System.Text.Encoding.UTF8));

                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                    int maxCount = (int)Math.Floor((double)((fileLength - startBytes) / pack)) + 1;

                    for (int i = 0; i < maxCount; i++)
                    {
                        if (_Response.IsClientConnected)
                        {
                            _Response.BinaryWrite(br.ReadBytes(pack));
                            Thread.Sleep(sleep);
                        }
                        else
                        {
                            i = maxCount;
                        }
                    }
                }
                catch
                {
                    return false;
                }
                finally
                {
                    br.Close();
                    myFile.Close();
                }
            }
            catch
            {
                return false;
            }
            return true;
        }
        #endregion

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　　以上代码亲测有效！附上本人测试用的代码(我下载的文件存放在服务器相对路径:down/学习笔记.rar，由于我的文件用于内部使用，故下载速度限制_speed给的很大)

protected void Button1_Click(object sender, EventArgs e)
    {
       
            string _fileName=“学习笔记.rar";//下载的文件名
            string _fullPath=MapPath("down/")+_fileName;//带全路径文件名
            long _speed=1000000000;//下载速度限制 字节/s
            try
            {
                FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                BinaryReader br = new BinaryReader(myFile);
                try
                {
                    Response.AddHeader("Accept-Ranges", "bytes");
                    Response.Buffer = false;
                    long fileLength = myFile.Length;
                    long startBytes = 0;

                    int pack = 10240; //10K bytes
                    //int sleep = 200;   //每秒5次   即5*10K bytes每秒
                    int sleep = (int)Math.Floor((double)(1000 * pack / _speed)) + 1;
                    if (Request.Headers["Range"] != null)
                    {
                        Response.StatusCode = 206;
                        string[] range = Request.Headers["Range"].Split(new char[] { '=', '-' });
                        startBytes = Convert.ToInt64(range[1]);
                    }
                    Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                    if (startBytes != 0)
                    {
                        Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength - 1, fileLength));
                    }
                    Response.AddHeader("Connection", "Keep-Alive");
                    Response.ContentType = "application/octet-stream";
                    Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode(_fileName, System.Text.Encoding.UTF8));

                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                    int maxCount = (int)Math.Floor((double)((fileLength - startBytes) / pack)) + 1;

                    for (int i = 0; i < maxCount; i++)
                    {
                        if (Response.IsClientConnected)
                        {
                            Response.BinaryWrite(br.ReadBytes(pack));
                        }
                        else
                        {
                            i = maxCount;
                        }
                    }
                }
                catch
                {
                   
                }
                finally
                {
                    br.Close();
                    myFile.Close();
                }
            }
            catch
            {
                
            }
    }

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　　本人较懒，没想去优化代码，能用就行。

原文地址：https://www.cnblogs.com/wendcn/p/12782325.html