!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: 2017/4/18 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: 2017/4/18 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));