Hello,Ajax

学习了Ajax技术，写了一个最简单的Ajax应用

<%@page contentType="text/html; charset=utf-8" language="java" import="java.sql.* " errorPage="" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'myHelloWorld.jsp' starting page</title>
    
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

    <script type="text/javascript">
        function ok(){
            var xmlhttp;
            if(window.XMLHttpRequest){
                //非ie
                xmlhttp=new XMLHttpRequest();
            }else if(window.ActiveXObject){
                try{
                    //ie
                    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
                }
                catch(e){
                    xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
                }
            }
            //设定回调函数
            xmlhttp.onreadystatechange=function(){
                if(xmlhttp.readyState==4){
                    if(xmlhttp.status==200){
                        //获取返回值
                        var msgWelcome=xmlhttp.responseText;
                        var msg=document.getElementById("msg");
                        msg.innerHTML=msgWelcome;
                    }
                }
            }
            //设定请求
            xmlhttp.open("get", "http://localhost:8080/LearnJava/myHelloWorld.do", true);
            //设定http头
            xmlhttp.setRequestHeader('Content-type','application/x-www-form-urlencoded');
            //发送请求
            xmlhttp.send(null);
        }
    </script>
  </head>
  
  <body>
    <span id="msg"></span><br>
    <input type="button" onclick="ok()" value="单击">
  </body>
</html>

View Code

关键代码：

<script type="text/javascript">
        function ok(){
            var xmlhttp;
            if(window.XMLHttpRequest){
                //非ie
                xmlhttp=new XMLHttpRequest();
            }else if(window.ActiveXObject){
                try{
                    //ie
                    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
                }
                catch(e){
                    xmlhttp=new ActiveXObject("Msxml2.XMLHTTP");
                }
            }
            //设定回调函数
            xmlhttp.onreadystatechange=function(){
                if(xmlhttp.readyState==4){
                    if(xmlhttp.status==200){
                        //获取返回值
                        var msgWelcome=xmlhttp.responseText;//获取response的输出值
                        var msg=document.getElementById("msg");
                        msg.innerHTML=msgWelcome;
                    }
                }
            }
            //设定请求
            xmlhttp.open("get", "http://localhost:8080/LearnJava/myHelloWorld.do", true);
            //设定http头
            xmlhttp.setRequestHeader('Content-type','application/x-www-form-urlencoded');
            //发送请求
            xmlhttp.send(null);
        }
    </script>

这里只是一个简单的ajax的应用，将servlet输出信息写入页面中。过程是：

首先创建一个xmlhttp对象，然后以get方法向servlet发送请求。当

onreadystatechange事件发生，则调用回调函数，向界面输出信息。