刚刚学习了ajax，初步整理一下知识点
1ajax是通过XmlHttpRequest对象和服务器进行通信的，它的优点是不用刷新页面就可以和服务器通信
2ajax三种传输数据的格式：
（1）xml :xml难解析，笨重，但是在全球上通用
（2）hmtl :不用解析可以直接放到文档中，通常用于更新很小一部分，但是不便于大量的数据，而且需要拼装
（3）JSON：小巧，又面向对象的特点，有很多第三方的jar包可以把json对象转换成为json字符串
3使用jquery完成对ajax的操作
（1）load方法可以用于hmtl中的任何一个元素，比如 a,div 元素，把结果直接加为到对应节点的子元素，通常用load加载html元素
var obj=...
var ur =。。
var arg ={"key ":"value"}
load(url,arg)
(2) $.get(url,arg,function(data){
})
url :ajax请求目标的urll
arg：传递参数，json格式
data:ajax响应成功后的对象，返回对象可能是xml,json hmtl
(3) $.get(url,function(data){
},"JSON")
data:ajax响应成功后的JSON对象
(4) $.post(url,"JSON")
(5) $.getJSON(url,function(data){
})
4下面粘贴使用ajax load方法的代码，达到局部刷新，至于helloajax.txt文件，内容自己写即可<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
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 'testAjax.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" src="script/jquery-1.6.2.js"></script>
<script type="text/javascript">
$(function(){
$("a").click(function(){
var url =this.href;
$("#content").load(url);
return false;
});
});
</script>
</head>
<body>
<a href="helloajax.txt"> hello ajax</a>
<div id="content"></div>
</body>
</html>
二 ：使用ajax jquery servlet 进行检验用户名
（1）jsp页面
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'v.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
<script type="text/javascript" src="${pageContext.request.contextPath}/script/jquery-1.6.2.js"></script>
<script type="text/javascript">
$(function(){
$(":input[name='username']").change(function(){
var val=$(this).val();
val=$.trim(val);
if(val!=""){
var url="${pageContext.request.contextPath}/valiateUsername";
var arg={"username":val,"date":new Date()};
$.post(url,function(data){
$("#message").html(data);
});
}
});
});
</script>
</head>
<body>
<form name="form1" id="form1">
用户名：<input type="text" name="username" id="username"/>
<br>
<div id="message"></div>
<br>
<input type="submit" value="注册"/>
<br>
</form>
</body>
</html>
(2)servlet代码
package com.lin.text;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class V extends HttpServlet {
public void destroy() {
super.destroy(); // Just puts "destroy" string in log
// Put your code here
}
public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException {
}
public void doPost(HttpServletRequest request,IOException {
List<String> usernames =Arrays.asList("AAA","BBB","CCC");
String username=request.getParameter("username");
System.out.print(username);
String result =null;
if(usernames.contains(username)){
result="<font color='red'>regist</font>";
}else{
result="<font color='red'>no</font>";
}
response.setContentType("text/html");
response.setCharacterEncoding("utf-8");
response.getWriter().print(result);
}
public void init() throws ServletException {
// Put your code here
}
}
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