异步文件下载(随写)

我起初是想实现大文件可继传异步下载,第一个版本异步,继传还没实现后继待续.
以下用了两种实现方法,注释部分是另一种实现方法
主要实现类

using System;
using System.Data;
using System.Web;
using System.Threading;
using System.IO;
using System.Collections;
using Spider.Model.XML;

namespace Spider.Model.AsyncNoCacheDown
{
   

    class AsynchOperation : IAsyncResult
    {
        private bool _completed;
        private Object _state;
        private AsyncCallback _callback;
        private HttpContext _context;

        bool IAsyncResult.IsCompleted { get { return _completed; } }
        WaitHandle IAsyncResult.AsyncWaitHandle { get { return null; } }
        Object IAsyncResult.AsyncState { get { return _state; } }
        bool IAsyncResult.CompletedSynchronously { get { return false; } }

        static Hashtable mimeMap = null;

        public AsynchOperation(AsyncCallback callback, HttpContext context, Object state)
        {
            _callback = callback;
            _context = context;
            _state = state;
            _completed = false;

            XMLHelper XmlHelper = new XMLHelper();
            mimeMap = XmlHelper.GetDataToHashtable(_context.Server.MapPath(@"/AsyncNoCacheDown/ModelConfig/MIMETypeTable.xml"), "MIMEITEM");
        }

        public void StartAsyncWork()
        {
            ThreadPool.QueueUserWorkItem(new WaitCallback(StartAsyncTask), null);
        }

        private void StartAsyncTask(Object workItemState)
        {
            _context.Response.Write("<p>Completion IsThreadPoolThread is " + Thread.CurrentThread.IsThreadPoolThread + "</p>\r\n");

            _context.Response.Write("Hello World from Async Handler!");

           

            string fileName = _context.Request.Params["DownFileName"];
            string filePath = "DownFiles/";

             _context.Response.Write(fileName);

            string path = _context.Server.MapPath(filePath+fileName);

            System.IO.FileInfo  toDownload = new System.IO.FileInfo(path);


            if (toDownload.Exists)
            {
                /**//*  块读取
                long DownFileBufferSize = 1000; // Read file buffer size.
                byte[] buffer = new byte[DownFileBufferSize]; // Read file buffer.
                long oldReaded = 0; // File already  read size. 
                */

                _context.Response.Clear();
                _context.Response.Charset = "UTF8";
                try
                {
                    _context.Response.ContentType = mimeMap[System.IO.Path.GetExtension(fileName).ToLower()].ToString();
                }
                catch
                {
                    _context.Response.ContentType = "application/octet-stream";
                }

                _context.Response.AddHeader("Content-Disposition", "attachment;filename=" + HttpUtility.UrlEncode("Spider_FileDown_"+fileName, System.Text.Encoding.UTF8));
                _context.Response.AddHeader("Content-Length", toDownload.Length.ToString());

                _context.Response.Write(_context.Response.ContentType);
               /**//* 块读取
                using(FileStream iStream   = File.OpenRead(path))
                {
                    long ReadFileLength =  iStream.Length;
                    long lengthRead = 0;
                    while(ReadFileLength > 0 && _context.Response.IsClientConnected)
                    {
                        lengthRead = iStream.Read(buffer, 0, (int)DownFileBufferSize);
                       
                      //  _context.Response.TransmitFile(path, oldReaded, DownFileBufferSize);

                        oldReaded = lengthRead + oldReaded;
                        ReadFileLength = ReadFileLength - lengthRead;
                    }
                }
                */
                _context.Response.TransmitFile(path);
            }
            else 
            {
                _context.Response.Write("<script language='javascript'>alert('File Not Exists!')</script>");
            }

            _context.Response.End();
           
            _completed = true;
            _callback(this);
        }
    }
}

HttpAsyncHandler 处理类

using System;
using System.Web;
using System.Threading;

namespace Spider.Model.AsyncNoCacheDown
{
    class HttpAsyncDownLoadHandler : IHttpAsyncHandler
    {

        public bool IsReusable { get { return false; } }

        public HttpAsyncDownLoadHandler()
        {
        }
        public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData)
        {
            context.Response.Write("<p>Begin IsThreadPoolThread is " + Thread.CurrentThread.IsThreadPoolThread + "</p>\r\n");

            AsynchOperation asynch = new AsynchOperation(cb, context, extraData);
            asynch.StartAsyncWork();
            return asynch;
        }

        public void EndProcessRequest(IAsyncResult result)
        {
        }

        public void ProcessRequest(HttpContext context)
        {
            throw new InvalidOperationException();
        }
    }
}

不要忘了在web.config文件中加入下面代码哟
<httpHandlers>
   <add verb="*" path="DownFile.axd" type="Spider.Model.AsyncNoCacheDown.HttpAsyncDownLoadHandler,Spider.Model"/>
  </httpHandlers>

仅供学习参考^o^