using System;

using System.Web;

using System.IO;

using System.Web.SessionState;

using System.Threading.Tasks;

public class DownLoadS3FileAsync : System.Web.HttpTaskAsyncHandler

{

    public void ProcessRequest(HttpContext context)

    {

        throw new NotImplementedException();

    }

    public override async Task ProcessRequestAsync(HttpContext context)

    {

        SystemError.CreateErrorLog("开始执行异步啦");

        await Task.Run(() =>

        {

            //调用下载方法

            Download(context);

        });

        SystemError.CreateErrorLog("调用异步完成啦");

    }

    public void Download(HttpContext context)

    {

        SystemError.CreateErrorLog("开始下载啦");

        //文件路径

        string key = context.Request.QueryString["key"];

        byte[] bFile = StorageService.Current.Download(key);

        //输出

        context.Response.Clear();

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

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

        context.Response.ContentType = contentType;

        context.Response.OutputStream.Write(bFile, , bFile.Length);

        context.Response.Flush();

        context.Response.End();

        SystemError.CreateErrorLog("下载结束了！");

    }

}