<div id="container"></div>
<script type="text/javascript">
  $(function () {
    function longPolling() {
      $.getJSON("/DateTime/GetTime", function (json) {
        $("#container").append(json.date + "<br/>");
        longPolling();
      });
    };
    longPolling();
  });
</script>

public class DateTimeController : AsyncController
  {
    public void GetTimeAsync()
    {
      //計(jì)時(shí)器，5秒種觸發(fā)一次Elapsed事件    
      System.Timers.Timer timer = new System.Timers.Timer(5000);
      //告訴.NET接下來(lái)將進(jìn)行一個(gè)異步操作    
      AsyncManager.OutstandingOperations.Increment();
      //訂閱計(jì)時(shí)器的Elapsed事件  
      timer.Elapsed += (sender, e) =>
      { //保存將要傳遞給GetTimeCompleted的參數(shù)        
        AsyncManager.Parameters["nowdate"] = e.SignalTime;
        //告訴ASP.NET異步操作已完成，進(jìn)行GetTimeCompleted方法的調(diào)用        
        AsyncManager.OutstandingOperations.Decrement();
      };
      //啟動(dòng)計(jì)時(shí)器    
      timer.Start();
    }
    public ActionResult GetTimeCompleted(DateTime nowdate)
    {
      return Json(new { date = nowdate.ToString("HH:mm:ss") + " Welecom " }, JsonRequestBehavior.AllowGet);
    }
  }