System.IO.Stream iStream = null;

// Buffer to read 10K bytes in chunk:

byte[] buffer = new Byte[];

// Length of the file:

int length;

// Total bytes to read:

long dataToRead;

// Identify the file to download including its path.

string filepath = "DownloadFileName";

// Identify the file name.

string filename = System.IO.Path.GetFileName(filepath);

try

{

    // Open the file.

    iStream = new System.IO.FileStream(filepath, System.IO.FileMode.Open,

                System.IO.FileAccess.Read, System.IO.FileShare.Read);

    // Total bytes to read:

    dataToRead = iStream.Length;

    Response.ContentType = "application/octet-stream";

    Response.AddHeader("Content-Disposition", "attachment; filename=" + filename);

    // Read the bytes.

    while (dataToRead > )

    {

        // Verify that the client is connected.

        if (Response.IsClientConnected)

        {

            // Read the data in buffer.

            length = iStream.Read(buffer, , );

            // Write the data to the current output stream.

            Response.OutputStream.Write(buffer, , length);

            // Flush the data to the HTML output.

            Response.Flush();

            buffer = new Byte[];

            dataToRead = dataToRead - length;

        }

        else

        {

            //prevent infinite loop if user disconnects

            dataToRead = -;

        }

    }

}

catch (Exception ex)

{

    // Trap the error, if any.

    Response.Write("Error : " + ex.Message);

}

finally

{

    if (iStream != null)

    {

        //Close the file.

        iStream.Close();

    }

}

protected void Btn_down_Click(object sender, EventArgs e)

    {

        if (ckl_ck.Items.Count > )

        {

            List<string> listFJ = new List<string>();//保存附件路径

            List<string> listFJName = new List<string>();//保存附件名字

            for (int i = ; i < ckl_ck.Items.Count; i++)

            {

                if (ckl_ck.Items[i].Selected)

                {

                    listFJ.Add(Server.MapPath("Resource/Help/") + ckl_ck.Items[i].Text);

                    listFJName.Add(ckl_ck.Items[i].Text);

                }

            }

            string time = DateTime.Now.Ticks.ToString();

            ZipFileMain(listFJ.ToArray(), listFJName.ToArray(), Server.MapPath("Resource/Help/" + time + ".zip"), );//压缩文件

            DownloadFile(Server.UrlEncode("附件.zip"), Server.MapPath("Resource/Help/" + time + ".zip"));//下载文件

        }

    }

    private void DownloadFile(string fileName, string filePath)

    {

        FileInfo fileInfo = new FileInfo(filePath);

        Response.Clear();

        Response.ClearContent();

        Response.ClearHeaders();

        Response.AddHeader("Content-Disposition", "attachment;filename=" + fileName);

        Response.AddHeader("Content-Length", fileInfo.Length.ToString());

        Response.AddHeader("Content-Transfer-Encoding", "binary");

        Response.ContentType = "application/octet-stream";

        Response.ContentEncoding = System.Text.Encoding.GetEncoding("gb2312");

        Response.WriteFile(fileInfo.FullName);

        Response.Flush();

        File.Delete(filePath);//删除已下载文件

        Response.End();

    }

    /// <summary>

    /// 压缩文件

    /// </summary>

    /// <param name="fileName">要压缩的所有文件（完全路径)</param>

    /// <param name="fileName">文件名称</param>

    /// <param name="name">压缩后文件路径</param>

    /// <param name="Level">压缩级别</param>

    public void ZipFileMain(string[] filenames, string[] fileName, string name, int Level)

    {

        ZipOutputStream s = new ZipOutputStream(File.Create(name));

        Crc32 crc = new Crc32();

        //压缩级别

        s.SetLevel(Level); // 0 - store only to 9 - means best compression

        try

        {

            int m = ;

            foreach (string file in filenames)

            {

                //打开压缩文件

                FileStream fs = File.OpenRead(file);//文件地址

                byte[] buffer = new byte[fs.Length];

                fs.Read(buffer, , buffer.Length);

                //建立压缩实体

                ZipEntry entry = new ZipEntry(fileName[m].ToString());//原文件名

                //时间

                entry.DateTime = DateTime.Now;

                //空间大小

                entry.Size = fs.Length;

                fs.Close();

                crc.Reset();

                crc.Update(buffer);

                entry.Crc = crc.Value;

                s.PutNextEntry(entry);

                s.Write(buffer, , buffer.Length);

                m++;

            }

        }

        catch

        {

            throw;

        }

        finally

        {

            s.Finish();

            s.Close();

        }

    }