!DOCTYPE HTML>
html>
head>
  title>反ajax推送/title>
  style>
    .send{color:#555;text-align: left;}
    .require{color:blue;text-align: right;}
    .content_box{text-align: center;margin: 20px;
          border: 1px solid #ddd;padding: 20px;}
  /style>
  script src="http://code.jQuery.com/jquery-1.11.2.min.js">/script>
/head>
body>
  div class="content_box" id="content_box_title" style="border: none;">消息框/div>
  div class="content_box" id="content_box">
  /div>
  div style="width: 450px;margin: 0 auto;">
    select id="username" style="font-size: 20px;">
      option value="1" selected="selected">1/option>
      option value="2">2/option>
    /select>
    input type="text" style="font-size: 20px;" value="" id="send_text">
    button id="btn_send" style="font-size: 20px;">发送/button>
    button id="btn_link" style="font-size: 20px">连接/button>
  /div>
  div class="error_tip" id="error_tip" style="color: red;">
  /div>
  script>
    $(function(){
      //发送消息
      $('#btn_send').click(function(){
        var send_text = $('#send_text').val();
        if(send_text.length = 0){
          $('#error_tip').html('不能输入空值');
        }else{
          send(send_text);
        }
      });
      //按回车键发送消息
      $('#send_text').on('keyup',function(e){
        if(e.keyCode == 13){
          $('#btn_send').trigger('click');
        }
      });
      //建立通讯链接
      $('#btn_link').click(function(){
        connect();
        var _this = $(this);
        _this.attr('disabled',true);
        _this.html('已连接');
      });
    });
    //建立通讯连接函数
    function connect(){
      $('#content_box_title').html($('#username').val()+'的消息窗口');
      $.ajax({
        data:{'user':$('#username').val()},
        url:'ajaxPush.PHP',
        type:'get',
        timeout:0,
        dataType:'json',
        success:function(data){
          $('#content_box').append('div class="require">'+data.msg+'/div>');
          connect();
        }
      });
    }
    //发送消息函数
    function send(massege){
      var user =$('#username').val();
      $.getJSON('write.php',{'msg':massege,'user':user},function(data){
        if(data.sf){
          $('#content_box').append('div class="send">'+massege+'/div>');
          $('#send_text').val('');
        }else{
          $('#error_tip').html('输入保存错误！');
        }
      });
    }
  /script>
/body>
/html>

?php
/**
 * Created by TXM.
 * Time: 2015/4/18 13:13
 * function:
 */
$filename = dirname(__FILE__).'/data.txt';
$isread_file = dirname(__FILE__).'/isread.txt';
$user = dirname(__FILE__).'/user.txt';
//写入消息，消息未读，谁发送的消息
file_put_contents($filename,$_GET['msg']);
file_put_contents($isread_file,'0');
file_put_contents($user,$_GET['user']);
echo json_encode(array('sf'=>true));

?php
/**
 * Created by TXM.
 * Time: 2015/4/18 13:12
 * function:
 */
$filename = dirname(__FILE__).'/data.txt';
$isread_file = dirname(__FILE__).'/isread.txt';
$userfile = dirname(__FILE__).'/user.txt';
$get_user = $_GET['user'] == '1'?'2':'1';
$msg='';
while(1){
  $msg = file_get_contents($filename);
  $isread = file_get_contents($isread_file);
  $user = file_get_contents($userfile);
  //是对方发送的消息，设置消息已读，退出循环。
  if($isread == '0'  $get_user == $user){
    file_put_contents($isread_file,'1');
    break;
  }
  sleep(1);
}
echo json_encode(array('msg'=>$msg));