AJAX制作JSON格式的实时更新数据的方法

之前有写过这样的文章，但是出现了几个问题，第一，如果每秒都像数据库发送请求势必会造成服务器的压力过大，第二，如果使用JS的话，是不可以取得系统时间的，因为JS运行在客户端，所以只能取得客户端时间，

如此的话，就需要在后台计算好时间差，然后前台得到时间差进行倒计时计算，并且更新数据

JS代码如下：

 var i = ;
    var ballNum = "";
    var flag = true;
    var timer_showCountDown = null;
    var leftTime;

    function showLeftTime(){
        ShowCountDown(leftTime);
    }

    /*-------------------------倒计时------------------------*/
    function ShowCountDown(sysTime) {
        console.warn(sysTime);
        var minute, second;
        if (isNaN(leftTime)) {
            leftTime = sysTime;
        } else {
            leftTime = sysTime;
        }
        minute = Math.floor(leftTime / ( * )) % ;//分
        second = Math.floor(leftTime / ) % ;//秒
        //把分钟和秒钟如果是一位数就变为两位数
        if (minute < ) {
            minute = "" + minute;
        }
        if (second < ) {
            second = "" + second;
        }
        //如果倒计时为负数，就设置为00：00
        if (leftTime < ) {
            //$("#dendtime").html("00" + ":" + "00");//倒计时的时间，M表示分钟，S表示秒钟

        } else {
            $("#dendtime").html(minute + ":" + second);//倒计时的时间，M表示分钟，S表示秒钟
        }
        leftTime = (parseInt(leftTime) - ).toString();
    }
    /*-------------------------倒计时 end------------------------*/

    /*-------------------------显示开奖结果------------------------*/
    function showWinNum(msg) {
        $("#dendtime").html("" + ":" + "");//倒计时的时间，M表示分钟，S表示秒钟

        var numb1 = msg[].getName.split("");//把期号分解成数组

        var numb2 = "";
        //把期号重新拆分处理
        for (var i = ; i < numb1.length; i++) {
            numb2 = numb1[numb1.length - i - ] + " " + numb2;
        }
        numb2 = numb2.substring(, numb2.length - );//得到新的期号

        var numb3 = msg[].getInfo.split(" ");//把球号分解成数组
        //这里暂时把跑号码球的方法变为直接显示号码球
        $("#num1").html("<li class=\"mt15\">" + numb3[] + "</li>");
        $("#num2").html("<li class=\"mt15\">" + numb3[] + "</li>");
        $("#num3").html("<li class=\"mt15\">" + numb3[] + "</li>");
        $("#num4").html("<li class=\"mt15\">" + numb3[] + "</li>");
        $("#num5").html("<li class=\"mt15\">" + numb3[] + "</li>");
        var numb4 = "";
        //把球号重新拆分处理
        for (var i = ; i < numb3.length; i++) {
            numb4 = numb3[numb3.length - i - ] + "----------------------------------------------------" + numb4;
        }

        numb4 = numb4.substring(, numb4.length - );//得到新的球号
        ballNum = msg[].getInfo;//将数据库里面取到的号码球的值存入一个变量

        $("#num").html(msg[].getName);//期号
        $("#nextNum").html(msg[].getNum);//下一期的期号
        //后台运行语音报号
        setTimeout(play("第" + numb2 + "期开奖号码是" + numb4 + "，感谢您的关注"), );
    }
    /*-------------------------显示开奖结果 end------------------------*/

    /*-------------------------语音报号------------------------*/
    swfobject.embedSWF("Share/sampleDemo.swf", "sampleDemo", "", "", "9.0.0", "Share/expressInstall.swf");
    function play(c) {
        var item = {};
        item.text = c;
        swfobject.getObjectById("sampleDemo").onSynthsize(item);
    }
    /*-------------------------语音报号 end------------------------*/

    function setTimeOutPost() {
        $.ajax({
            type: "post",
            url: "/Lottery/DoDataMethod/GetKLCData.ashx",
            dataType: "json",
            async: true,
            success:
                function (msg) {
                    leftTime = msg[].getSysTime;
                    //首先倒计时
                    if (timer_showCountDown != null) {
                        clearInterval(timer_showCountDown);
                    }
                    timer_showCountDown = setInterval(showLeftTime, );

                    //如果开奖结果有变化，则重新显示并报号
                    if (ballNum != msg[].getInfo) {
                        showWinNum(msg);
                    }

                    //10秒调用一次AJAX方法更新数据
                    setTimeout(setTimeOutPost, );
                }
            ,
            error: function (req) {
                //alert(req.readyState);//出错时提示出错状态
            }
        });
    }
    window.onload = function () {
        setTimeOutPost();
    }

后台代码如下：

 context.Response.ContentType = "application/json";

        string[] Info = new string[];
        string ConStr = ConfigurationManager.AppSettings["ConnectionString"].ToString();
        //得到上期开出的数据
        string GetDate = @"
                                SELECT
                                   TOP 1
                                   [ID]
                                  ,[LotteryID]
                                  ,[Name]
                                  ,[StartTime]
                                  ,[EndTime]
                                  ,[ChaseExecuted]
                                  ,[IsOpened]
                                  ,[WinLotteryNumber]
                                  ,[OpenOperatorID]
                                  ,[State]
                                  ,[StateUpdateTime]
                                  ,[OpenAffiche]
                              FROM [T_Isuses]
                              WHERE EndTime<getdate() and WinLotteryNumber<>'' and [IsOpened]=1
                              ORDER BY [EndTime] desc
                                ";

        //得到本期的时间
        string GetNowTime = @"
                                        SELECT
                                        TOP 1
                                        [ID]
                                        ,[LotteryID]
                                        ,[Name]
                                        ,[StartTime]
                                        ,[EndTime]
                                        ,[ChaseExecuted]
                                        ,[IsOpened]
                                        ,[WinLotteryNumber]
                                        ,[OpenOperatorID]
                                        ,[State]
                                        ,[StateUpdateTime]
                                        ,[OpenAffiche]
                                    FROM [T_Isuses]
                                    WHERE IsOpened=0 and EndTime>(
                                        SELECT
                                            TOP 1
                                            [EndTime]
                                        FROM [T_Isuses]
                                        WHERE EndTime<getdate() and WinLotteryNumber<>'' and [IsOpened]=1 and LotteryID=79
                                        ORDER BY [EndTime] desc
                                    ) and LotteryID=79 order by Name
                                ";

        using (SqlConnection conn = new SqlConnection(ConStr))
        {
            conn.Open();
            SqlCommand comm = new SqlCommand(GetDate, conn);
            SqlDataReader reader = comm.ExecuteReader();

            while (reader.Read())
            {
                Info[] = reader["WinLotteryNumber"].ToString();
                Info[] = reader["Name"].ToString();
                Info[] = (Convert.ToInt32(Info[].ToString().Substring(, )) + ).ToString();
                if(Info[].Length<=)
                {
                    Info[] = "" + Info[];
                }
            }
            reader.Close();
        }
        using (SqlConnection Nowconn = new SqlConnection(ConStr))
        {
            Nowconn.Open();
            SqlCommand nowComm = new SqlCommand(GetNowTime, Nowconn);
            SqlDataReader NowReader = nowComm.ExecuteReader();
            while (NowReader.Read())
            {
                Info[] = NowReader["EndTime"].ToString();
            }
            NowReader.Close();
        }
        TimeSpan dtime = Convert.ToDateTime(Info[]) - Convert.ToDateTime(System.DateTime.Now);//开奖时间减去系统时间
        var outTime = (dtime.Minutes * ) + (dtime.Seconds * ) + ;//结果换算成毫秒数
        string obj = "[{\"getInfo\":\"" + Info[] + "\",\"getName\":\"" + Info[] + "\",\"getNum\":\"" + Info[] + "\",\"getSysTime\":\"" + outTime + "\"}]";
        context.Response.Write(obj);

需要注意的是JSON格式的数据返回的时候要带中括号，不然前台页面会找不到数据的