上传文件时，定时调用ajax读取缓存信息，如果有session存在，就要等到上传完成服务器才会响应ajax发出的请求，这是什么原因？

xiayun201225 2012-10-08 04:32:47

背景：上传文件时，想要在页面上显示上传进度。在页面中放了一个装有FileUpload的iframe，选择文件之后，提交iframe，上传文件，并在缓存里循环更新上传进度。同时定时调用ajax去读取缓存信息，更新到页面上。

问题：如果在session中有任何内容存在，则只有等到上传完成才会响应ajax发出的请求。如果session中没有内容，则可以正常显示。请教各位大侠，这是什么原因？

代码：
主页面UploadPic.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="UploadPic.aspx.cs" Inherits="UploadPic" %>



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">



<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

    <title>无标题页</title>

</head>

<script type="text/javascript">

var form;

var intervalID = 0;

function startUpload()

{

     var msg = document.getElementById("msg");      

     var url = "progressmonitor.aspx";  

     var postStr = "guid=<%=myGuid %>";  



     //实例化Ajax  

     var ajax = false;  

     if(window.XMLHttpRequest)   

     {   

         ajax = new XMLHttpRequest();  

         if (ajax.overrideMimeType)   

         {   

             ajax.overrideMimeType("text/xml");  

         }  

     }  

     else if (window.ActiveXObject)   

     {   

         try  

         {  

             ajax = new ActiveXObject("Msxml2.XMLHTTP");  

         }   

         catch (e)   

         {  

             try  

             {  

                ajax = new ActiveXObject("Microsoft.XMLHTTP");  

             }   

            catch (e) {}  

         }  

     }  

     if (!ajax)   

     {   // 异常，创建对象实例失败  

        window.alert("不能创建XMLHttpRequest对象实例.");  

       return false;  

     }   

        



     intervalID = window.setInterval(function(){

     ajax.open("POST", url, true);  

     ajax.setRequestHeader("Content-Type","application/x-www-form-urlencoded");  

     ajax.send(postStr);  }, 500);

   

     //获取执行状态  

     ajax.onreadystatechange = function()   

     {   

        //如果执行状态成功，那么就把返回信息写到指定的层里  

         if (ajax.readyState == 4 && ajax.status == 200)   

        {   

            msg.innerHTML = ajax.responseText;   

        }   

    }   

    

    form.submit();

}



function register(form){            

    this.form = form;

} 



function onComplete(type){

    // 自动消失

    window.clearInterval(intervalID);

}        

</script>

<body>

<div id="msg">

        </div>

    <form id="form1" runat="server">

    <div>

        <asp:HiddenField ID="hfguid" runat="server" />

        <iframe id="uploadFrame" frameborder="0" scrolling="no" src="upload.aspx"></iframe>

    </div>

    </form>

</body>

</html>

后台

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;



public partial class UploadPic : System.Web.UI.Page

{

    protected string myGuid;

    protected void Page_Load(object sender, EventArgs e)

    {

        if (!IsPostBack)

        {

            Session["aa"] = 3;

            myGuid = System.Guid.NewGuid().ToString();

            this.hfguid.Value = myGuid;

        }

    }

}

内嵌的iframe：upload.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="upload.aspx.cs" Inherits="upload" %>



<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">



<html xmlns="http://www.w3.org/1999/xhtml">

<head runat="server">

    <title>无标题页</title>

</head>

<body>

    <form id="form1" runat="server">

    <div>

        <asp:FileUpload ID="fileUpload" runat="server" Width="100%" onchange="upload(this);" />

        <asp:HiddenField ID="hfguid" runat="server" />

    </div>

    </form>

</body>

</html>

<script type="text/javascript">

window.onload = function() {

    var myform = document.getElementById("form1");

    window.parent.register(myform);

    document.getElementById("hfguid").value = parent.document.getElementById("hfguid").value;

}

        

function upload(ob)

{

    parent.startUpload();

}

</script>

后台

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using System.IO;

using System.Web.Caching;

using System.Threading;

using System.Web.UI.MobileControls;

using System.Collections.Generic;



public partial class upload : System.Web.UI.Page

{

    private const int BUFFERSIZE = 5000;

    protected void Page_Load(object sender, EventArgs e)

    {

        if (IsPostBack)

        {

            uploadFile(this.fileUpload.PostedFile);

        }

    }



    protected void uploadFile(HttpPostedFile postedFile)

    {

        string filePath = @"C:\upload file\";

        if (!Directory.Exists(filePath))

        {

            Directory.CreateDirectory(filePath);

        }



        string guid = this.hfguid.Value.ToString();



        //object fileObj = HttpContext.Current.Cache[guid];

        //if (fileObj != null)

        //{

        //    HttpContext.Current.Cache.Remove(guid);

        //}



        List<FileInfo> infos = Cache[guid] as List<FileInfo>;

        if (infos == null)

        {

            infos = new List<FileInfo>();

        }



        FileInfo info = new FileInfo();

        info.FileName = postedFile.FileName;

        info.TotalLength = postedFile.ContentLength;

        info.CurrentLength = 0;

        info.UploadPath = filePath;

        infos.Add(info);



        HttpContext.Current.Cache.Add(guid, infos, null, DateTime.Now.AddDays(1), TimeSpan.Zero, CacheItemPriority.AboveNormal, null);



        FileStream fStream = new FileStream(filePath + postedFile.FileName, FileMode.Create);

        Stream reader = postedFile.InputStream;

        byte[] buffer = new byte[BUFFERSIZE];

        int len = reader.Read(buffer, 0, BUFFERSIZE);



        while (len > 0)

        {

            fStream.Write(buffer, 0, len);

            info.CurrentLength += len;

            //模拟延时用，实际应用的时候注销他

            Thread.Sleep(100);

            HttpContext.Current.Cache[guid] = infos;

            len = reader.Read(buffer, 0, BUFFERSIZE);

        }



        reader.Close();

        fStream.Close();



        const string js = "window.parent.onComplete('success');";

        ScriptManager.RegisterStartupScript(this, this.GetType(), "progress", js, true);

    }



}

ajax请求：progressmonitor.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="progressmonitor.aspx.cs" Inherits="progressmonitor" %>





        <table>

            <tr>

                <td>

                    图片名

                </td>

                <td style="width:200px;">

                    上传进度

                </td>

            </tr>

            

            <%=uploadinfo%>

        </table>

后台

using System;

using System.Collections;

using System.Configuration;

using System.Data;

using System.Linq;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.HtmlControls;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

using System.Xml.Linq;

using System.Threading;

using System.Collections.Generic;



public partial class progressmonitor : System.Web.UI.Page

{

    protected string uploadinfo = string.Empty;



    protected void Page_Load(object sender, EventArgs e)

    {

        string guid = Request.Params["guid"].ToString();

        List<FileInfo> infos = HttpContext.Current.Cache[guid] as List<FileInfo>;

        if (infos == null)

        {

            return;

        }



        for (int i = 0; i < infos.Count; i++)

        {

            int percent = (int)Math.Ceiling((double)infos[i].CurrentLength / (double)infos[i].TotalLength * 100);

            uploadinfo += "<tr><td><div>" + infos[i].FileName + "</div></td><td><div style=\"width:" + percent + "%; background-color:Green;\"></div></td></tr>";

        }

    }

}