ajax的两种实现

 1 <script type="text/javascript"
 2     src="${pageContext.request.contextPath}/js/jquery.min.js">
 3     
 4 </script>
 5 <script type="text/javascript">
 6     setInterval("AjaxJquery()", 3000);
 7     function AjaxJquery() {//通过jQuery发起请求
 8         $.ajax({
 9             url : "${pageContext.request.contextPath}/ajax_do",
10             type : "get",
11             error:function(){
12                 alert("请求失败");
13             },
14             success : function(msg) {
15                 $("#msg").append(msg);
16             }
17         });
18     }
19 </script>

 1 <script type="text/javascript"
 2     src="${pageContext.request.contextPath}/js/jquery.min.js">
 3     
 4 </script>
 5 <script type="text/javascript">
 6     setInterval("Ajax()", 3000);
 7 function Ajax(){//通过XMLHttpRequest发起请求
 8         var xmlhttp = new XMLHttpRequest();//创建XMLHttpRequest对象
 9         xmlhttp.open("post","${pageContext.request.contextPath}/ajax_do",true);
10         xmlhttp.send();
11         //接收服务器返回数据
12         xmlhttp.onreadystatechange=function(){
13             if(xmlhttp.readyState==4&&xmlhttp.status==200){
14                 //得到服务端响应
15                 $("#msg").append(xmlhttp.responseText);
16             }
17         }
18     }
19 </script>