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。