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>

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。

巴特西

Hello,Ajax

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