/// summary>
/// ServerPush1 的摘要说明
/// /summary>
public class ServerPush1 : IHttpHandler
{
  public void ProcessRequest(HttpContext context)
  {
   context.Response.ContentType = "application/json";
   string action = context.Request["action"];
   if (action == "send")//发送
   {
    string me = context.Request["me"];
    string toUserName = context.Request["toUserName"];
    string msg = context.Request["msg"];
    SQLHpler.ExecuteNonQuery("INSERT INTO T_Msgs(FromUserName,ToUserName,Msg) VALUES(@FromUserName,@ToUserName,@Msg)", new SqlParameter("@FromUserName", me),
     new SqlParameter("@ToUserName", toUserName),
     new SqlParameter("@Msg", msg));
    context.Response.Write(new JavaScriptSerializer().Serialize(new { Status = "ok" }));
   }
   else if (action == "receive")
   //登陆，并持续查询、接收对方发过来的数据
   {
    //做一个简单的例子，以ServerPush1.ashx?me=sean
    //请把发给sean的消息发给我一条
    string me = context.Request["me"];
    while (true)
    {
     DataTable dt = SQLHpler.ExecuteQuery("SELECT TOP 1 * FROM T_Msgs WHERE ToUserName=@ToUserName",new SqlParameter("@ToUserName", me));
     if (dt.Rows.Count = 0)
     {
      Thread.Sleep(500);//没找到，休息500ms再查询，这样避免对数据库的查询压力，和占用WEB服务器CPU资源
      continue;//下一次while
     }
     else
     {
      DataRow row = dt.Rows[0];
      long id = (long)row["Id"];
      string fromUserName = (string)row["FromUserName"];
      string msg = (string)row["Msg"];
      //查询完之后要删除消息，否则会出现死循环，不停的给页面输出同一个消息
      SQLHpler.ExecuteNonQuery("DELETE FROM T_Msgs WHERE Id=@Id",new SqlParameter("@Id",id));
      //创建一个匿名对象，将查询到的数据存到里面
      var data = new { FromUserName = fromUserName, Msg = msg, Id = id };
      string json = new JavaScriptSerializer().Serialize(data);//将匿名对象转换为json
      context.Response.Write(json);//将请求结果以json格式返回
      break;
     }
    }
   }
   else
   {
    throw new Exception("action错误");
   }
}

!DOCTYPE html>
html xmlns="http://www.w3.org/1999/xhtml">
head>
meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
title>/title>
script type="text/javascript" src="jquery-1.8.3.min.js">/script>
script type="text/javascript">
var rev = function () {
 var mine = $('#me').val();
 $.ajax({
  type: 'post', url: 'serverPush1.ashx',
  data: { action: 'receive', me: mine },//传给serverPush.ashx根据me查找发给me的消息
  success: function (data) {
   $('#ulMsg').append($('li>' + data.FromUserName + '对我说：' + data.Msg + '/li>'));
   rev();//收到消息后再向服务器请求数据，再给我一条消息
  },
  error: function () {
   rev();
   //哪怕网络请求失败（比如用户网络故障），也再次发送请求
  }
 });
};
$(function () {
 //发送
 $('#btnSend').click(function () {
  var myName = $('#me').val();
  var toUserName = $('#toUserName').val();
  var msg = $('#msgContext').val();
  $.ajax({
   type: 'post', url: 'serverPush1.ashx',
   data: { action: 'send', me: myName, toUserName: toUserName, msg: msg },//根据用户输入的信息，传到服务端ServerPush.ashx进行插入操作
   success: function (data) {
    if (data.Status == 'ok') {//如果发送成功，
     $('#ulMsg').append($('li>我对' + toUserName + '说：' + msg + '/li>'));
     $('#msgContext').val('');
    }
    else {
     alert('发送出错，返回报文无法识别');
    }
   },
   error: function () {
    alert('发送出错');
   }
  });
 });
 //登陆，接收数据
 $('#btnLogin').click(function () {
  rev();
  $(this).attr("disabled", "disabled");
 });
 /*
 $('#btnLogin').click(function () {//接收
  var mine = $('#me').val();
  $.ajax({
   type: 'post', url: 'serverPush1.ashx',
   data: { action: 'receive', me: mine },
   //传给serverPush.ashx根据me查找发给me的消息
   success: function (data) {
    $('#ulMsg').append($('li>' + data.toUserName + '对我说：' + data.msg + '/li>'));
   },
   error: function () {
    alert('接收失败');
   }
  });
 });*/
});
/script>
/head>
body>
 发送人：input type="text" id="me" />input type="button" id="btnLogin" value="登陆" style=""/>br />
 接收人：input type="text" id="toUserName" />br />
 输入消息：input type="text" id="msgContext" />input type="button" id="btnSend" value="发送" />br />
 聊天记录：br />
 ul id="ulMsg">
 /ul>
/body>
/html>