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利用Jquery实现http长连接(LongPoll) {转}

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

<!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>
    <script type="text/javascript" src="http://www.mamicode.com/script/jquery-1.2.6.js"></script>
    <script type="text/javascript">
        $(document).ready(function(){
            $("#Button1").bind("click",{btn:$("#Button1")},function(evdata){
                $.ajax({
                    type:"POST",
                    url:"JqueryAjaxLongPoll.aspx",
                    dataType:"json",
                    timeout:10000,
                    data:{ajax:"1",time:"10000"},
                    success:function(data,textStatus){
                            //alert("ok!");
                            evdata.data.btn.click();
                    },
                    complete:function(XMLHttpRequest,textStatus){
                            if(XMLHttpRequest.readyState=="4"){
                                alert(XMLHttpRequest.responseText);
                            }
                    },
                    error: function(XMLHttpRequest,textStatus,errorThrown){
                            //$("#ajaxMessage").text($(this).text()+" out!")
                            alert("error:"+textStatus);
                            if(textStatus=="timeout")
                                evdata.data.btn.click();
                    }
                });
            });

            /*$("#ajaxMessage").ajaxStart(function(){
                $(this).text("准备建立请求.readyState0:");
            });
            $("#ajaxMessage").ajaxSend(function(evt, request, settings){
                $(this).text("开始请求,准备发送数据.readyState1:"+request.readyState);
            });
            $("#ajaxMessage").ajaxComplete(function(event,request, settings){
                if(request.status==200)
                    $(this).text("请求完成.readyState4:"+request.readyState);
            });
            $("#ajaxMessage").ajaxStop(function(){
                $(this).text("请求结束.");
            });*/
        });
    </script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <input id="Button1" type="button" value="http://www.mamicode.com/AjaxLongPoll" />
        <label id="ajaxMessage"></label>
    </div>
    </form>
</body>
</html>

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Threading;

public partial class JqueryAjaxLongPoll : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.Form["ajax"] == "1")
        {
            //Response.End();
            int time = Convert.ToInt32(Request.Form["time"]);
            DateTime date1 = DateTime.Now.AddMilliseconds((double)time);
            bool ready = false;
            while (Response.IsClientConnected)
            {
                Thread.Sleep(3000);
                if (DateTime.Compare(date1, DateTime.Now) < 0)
                {
                    Response.End();
                    break;
                }
                //ready = true;
                if (ready)
                {
                    Response.Write("SetValue(‘" + DateTime.Now.ToString() + "‘)");
                    //Response.Flush();
                    Response.End();
                    break;
                }
                else
                {

                }
            }
        }
        else
        {
            if (!Page.IsPostBack)
            {

            }
        }
    }
}

思路:

 

 

利用jquery,很方便的就能实现ajax,上面设置了ajax的timeout时间,由于设置了timeout将会造成不能保持长连接,到了时间ajax自动会报“超时”的错误,也就是会调用error方法,此时textStatus=="timeout",timeout后重新进行ajax请求。服务器接受ajax请求的时候,会接收一个超时时间的值,超时的情况下服务器端的处理也立即停止。当客户端成功获取返回结果时,也会立即进行新的ajax请求,如此循环。

为什么要设置客户端的ajax超时值呢?因为服务器为了保持请求(阻塞请求),必须有一个无限循环,循环的结束条件就是获取到了返回结果,如果客户端关闭了(客户端浏览器的关闭不会发消息给服务器),服务器无法知道客户端已经关了,这个请求没必要处理下去了。最终会造成资源过度浪费,只要用一个折中的办法,限制超时时间。

可以不必设置客户端ajax的超时时间,但进行请求的时候传递一个超时值给服务器,服务器在处理的时候,如果超时时间到了的话,还没有客户端需要的结果,这时传递一个超时信息给客户端,客户端接收到了此信息,根据情况重新进行ajax请求。XMLHttpRequest没有超时的参数,Jquery用window.setTimeout自己封装的(到了定时时间运行超时处理方法,和XMLHttpRequest结束方法)。可以根据这个思路来改变一下,IBM上介绍的LONG POLL好像也是这样的。

$(document).ready(function(){
            $("#Button1").bind("click",{btn:$("#Button1")},function(evdata){
                $.ajax({
                    type:"POST",
                    url:"JqueryAjaxLongPoll.aspx",
                    dataType:"json",
                    data:{ajax:"1",time:"6000000"},
                    success:function(data,textStatus){
                            //成功
                            if(data.success=="1"){
                                //客户端处理
                                //...
                                ///重新请求
                                evdata.data.btn.click();
                            }
                            //超时
                            if(data.success=="0"){
                                evdata.data.btn.click();
                            }
                    },
                    complete:function(XMLHttpRequest,textStatus){
                            if(XMLHttpRequest.readyState=="4"){
                                alert(XMLHttpRequest.responseText);
                            }
                    },
                    error: function(XMLHttpRequest,textStatus,errorThrown){
                            //$("#ajaxMessage").text($(this).text()+" out!")
//                            alert("error:"+textStatus);
//                            if(textStatus=="timeout")
                                evdata.data.btn.click();
                    }
                });
            });

后台代码变更后:
if (Request.Form["ajax"] == "1")
        {
            int time = Convert.ToInt32(Request.Form["time"]);
            DateTime date1 = DateTime.Now.AddMilliseconds((double)time);
            bool ready = false;
            while (Response.IsClientConnected)
            {
                Thread.Sleep(3000);
                if (DateTime.Compare(date1, DateTime.Now) < 0)
                {
                    Response.Write("{success:‘0‘}");
                    Response.End();
                    break;
                }
                //此处进行请求处理,有结果了置ready = true
                //ready = true;
                if (ready)
                {
                    Response.Write("{success:‘1‘}");
                    Response.End();
                    break;
                }
            }
        }
        else
        {
            if (!Page.IsPostBack)
            {

            }
        }

上面的方法应该就可以满足要求了,具体的超时时间可以根据情况来设置。这也是我根据IBM上介绍的“server push”思路,来实现了其中的一种,也不知道有没有问题,还请大家多多赐教。