AJAX实例入门

一、开门见山

这些时间，瞎子也看得见，AJAX正大踏步的朝我们走来。不管我们是拥护也好，反对也罢，还是视而不见，AJAX像一阵潮流，席转了我们所有的人。
关于AJAX的定义也好，大话也好，早有人在网上发表了汗牛充栋的文字，在这里我也不想照本宣科。
只想说说我感觉到的一些优点，对于不对，大家也可以和我讨论：
首先是异步交互，用户感觉不到页面的提交，当然也不等待页面返回。这是使用了AJAX技术的页面给用户的第一感觉。
其次是响应速度快，这也是用户强烈体验。
然后是与我们开发者相关的，复杂UI的成功处理，一直以来，我们对B/S模式的UI不如C/S模式UI丰富而苦恼。现在由于AJAX大量使用JS，使得复杂的UI的设计变得更加成功。
最后，AJAX请求的返回对象为XML文件，这也是一个潮流，就是WEB SERVICE潮流一样。易于和WEB SERVICE结合起来。
好了，闲话少说，让我们转入正题吧。
我们的第一个例子是基于Servlet为后台的一个web应用。

二、基于Servlet的AJAX

第一个例子是关于关联选择框的问题，如图：

这是一个很常见的UI，当用户在第一个选择框里选择ZHEJIANG时，第二个选择框要出现ZHEJIANG的城市；当用户在第一个选择框里选择JIANGSU时，第二个选择框里要出现JIANGSU的城市。
首先，我们来看配置文件web.xml，在里面配置一个servlet，跟往常一样：
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

<servlet>
<servlet-name>SelectCityServlet</servlet-name>
<servlet-class>com.stephen.servlet.SelectCityServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>SelectCityServlet</servlet-name>
<url-pattern>/servlet/SelectCityServlet</url-pattern>
</servlet-mapping>

</web-app>

然后，来看我们的JSP文件：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>MyHtml.html</title>

<Meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<Meta http-equiv="description" content="this is my page">



</head>
<script type="text/javascript">
function getResult(stateVal) {
var url = "servlet/SelectCityServlet?state="+stateVal;
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
}else if (window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
}
if(req){
req.open("GET",url,true);
req.onreadystatechange = complete;
req.send(null);
}
}
function complete(){
if (req.readyState == 4) {
if (req.status == 200) {
var city = req.responseXML.getElementsByTagName("city");
//alert(city.length);
var str=new Array();
for(var i=0;i<city.length;i++){
str[i]=city[i].firstChild.data;
}
//alert(document.getElementById("city"));
buildSelect(str,document.getElementById("city"));
}
}
}
function buildSelect(str,sel) {
sel.options.length=0;
for(var i=0;i<str.length;i++) {
sel.options[sel.options.length]=new Option(str[i],str[i])
}
}
</script>
<body>
<select name="state" onChange="getResult(this.value)">
<option value="">Select</option>>
<option value="zj">ZEHJIANG</option>>
<option value="zs">JIANGSU</option>>
</select>
<select id="city">
<option value="">CITY</option>
</select>
</body>
</html>

第一眼看来，跟我们平常的JSP没有两样。仔细一看，不同在JS里头。
我们首先来看第一个方法：getResult(stateVal)，在这个方法里，首先是取得XmlHttpRequest；然后设置该请求的url：req.open("GET",true);接着设置请求返回值的接收方法：req.onreadystatechange = complete;该返回值的接收方法为——complete();最后是发送请求：req.send(null);
然后我们来看我们的返回值接收方法：complete()，这这个方法里，首先判断是否正确返回，如果正确返回，用DOM对返回的XML文件进行解析。关于DOM的使用，这里不再讲述，请大家参阅相关文档。得到city的值以后，再通过buildSelect(str,sel)方法赋值到相应的选择框里头去。

最后我们来看看Servlet文件：
import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class SelectCityServlet extends HttpServlet {

public SelectCityServlet() {
super();
}

public void destroy() {
super.destroy();
}

public void doGet(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException {
response.setContentType("text/xml");
response.setHeader("Cache-Control","no-cache");
String state = request.getParameter("state");
StringBuffer sb=new StringBuffer("<state>");
if ("zj".equals(state)){
sb.append("<city>hangzhou</city><city>huzhou</city>");
} else if("zs".equals(state)){
sb.append("<city>nanjing</city><city>yangzhou</city><city>suzhou</city>");
}
sb.append("</state>");
PrintWriter out=response.getWriter();
out.write(sb.toString());
out.close();
}
}
这个类也十分简单，首先是从request里取得state参数，然后根据state参数生成相应的XML文件，最后将XML文件输出到PrintWriter对象里。
到现在为止，第一个例子的代码已经全部结束。是不是比较简单？我们进入到第二个实例吧！
这次是基于JSP的AJAX的一个应用。

三、基于JSP的AJAX

这个例子是关于输入校验的问题，我们知道，在申请用户的时候，需要去数据库对该用户性进行唯一性确认，然后才能继续往下申请。如图：

这种校验需要访问后台数据库，但又不希望用户在这里提交后等待，当然是AJAX技术大显身手的时候了。
首先来看显示UI的JSP:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Check.html</title>

<Meta http-equiv="keywords" content="keyword1,keyword3">
<Meta http-equiv="description" content="this is my page">



</head>
<script type="text/javascript">
var http_request = false;
function send_request(url) {//初始化、指定处理函数、发送请求的函数
http_request = false;
//开始初始化XMLHttpRequest对象
if(window.XMLHttpRequest) { //Mozilla 浏览器
http_request = new XMLHttpRequest();
if (http_request.overrideMimeType) {//设置MiME类别
http_request.overrideMimeType('text/xml');
}
}
else if (window.ActiveXObject) { // IE浏览器
try {
http_request = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
http_request = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {}
}
}
if (!http_request) { // 异常，创建对象实例失败
window.alert("不能创建XMLHttpRequest对象实例.");
return false;
}
http_request.onreadystatechange = processRequest;
// 确定发送请求的方式和URL以及是否同步执行下段代码
http_request.open("GET",true);
http_request.send(null);
}
// 处理返回信息的函数
function processRequest() {
if (http_request.readyState == 4) { // 判断对象状态
if (http_request.status == 200) { // 信息已经成功返回，开始处理信息
alert(http_request.responseText);
} else { //页面不正常
alert("您所请求的页面有异常。");
}
}
}
function userCheck() {
var f = document.form1;
var username = f.username.value;
if(username=="") {
window.alert("The user name can not be null!");
f.username.focus();
return false;
}
else {
send_request('check1.jsp?username='+username);
}
}

</script>
<body>
<form name="form1" action="" method="post">
User Name:<input type="text" name="username" value=""> 
<input type="button" name="check" value="check" onClick="userCheck()">
<input type="submit" name="submit" value="submit">
</form>
</body>
</html>

所有的JS都跟上一个例子一样，不同的只是对返回值的操作，这次是用alert来显示：alert(http_request.responseText);
我们来看处理逻辑JSP:
<%@ page contentType="text/html; charset=gb2312" language="java" errorPage="" %>
<%
String username= request.getParameter("username");
if("educhina".equals(username)) out.print("用户名已经被注册，请更换一个用户名。");
else out.print("用户名尚未被使用，您可以继续。");
%>

非常简单，先取得参数，然后作处理，最后将结果打印在out里。
我们的第三个例子仍然以这个唯一性校验为例子，这次结合Struts开发框架来完成AJAX的开发。

四、基于Struts的AJAX

首先，我们仍然是对Struts应用来做配置，仍然是在struts-config,xml文件里做配置，如下：
<action type="com.ajax.CheckAction"
scope="request" path="/ajax/check">
<forward name="success" path="/check.jsp"/>
</action>

跟普通的Struts应用的配置一样，只是没有ActionForm的配置。
下面是Action类：
package com.ajax;

import java.io.PrintWriter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.DynaActionForm;

/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class CheckAction extends Action
{
public final ActionForward execute(ActionMapping mapping,ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception
{
System.out.println("haha...............................");
String username= request.getParameter("username");
System.out.println(username);
String retn;
if("educhina".equals(username)) retn = "Can't use the same name with the old use,pls select a difference...";
else retn = "congraducation!you can use this name....";
PrintWriter out=response.getWriter();
out.write(retn);
out.close();
return mapping.findForward("success");
}
public static void main(String[] args)
{
}
}

我们可以看到里面的逻辑跟上例中Servlet里的逻辑一样。最后，我们来看看JSP:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Check.html</title>

<Meta http-equiv="keywords" content="keyword1,true);
http_request.send(null);
}
// 处理返回信息的函数
function processRequest() {
if (http_request.readyState == 4) { // 判断对象状态
if (http_request.status == 200) { // 信息已经成功返回，开始处理信息
alert(http_request.responseText);
} else { //页面不正常
alert("您所请求的页面有异常。");
}
}
}
function userCheck() {
var f = document.forms[0];
var username = f.username.value;
if(username=="") {
window.alert("The user name can not be null!");
f.username.focus();
return false;
}
else {
send_request('ajax/check.do?username='+username);
}
}

</script>
<body>
<form name="form1" action="" method="post">
User Name:<input type="text" name="username" value=""> 
<input type="button" name="check" value="check" onClick="userCheck()">
<input type="submit" name="submit" value="submit">
</form>
</body>
</html>

我们可以看到，JSP基本是一样的，除了要发送的url：ajax/check.do?username='+username。
最后，我们来看一个基于Struts和AJAX的复杂一些的例子，如果不用AJAX技术，UI的代码将十分复杂。

五、一个复杂的实例

我们先来看看UI图：

这是一个比较复杂的级联：一共八个列表框，三个下拉框。从第一个列表框里选择到第二个列表框里后，第一个选择框里的选项是第二个列表框的选择；然后，在第一个选择框里选择以后，与选择值关联的一些选项出现在第三个列表框里。从第三个列表框里选择选项到第四个列表框里，同样，第二个选择框的选项也是第四个列表框的选项；如果对第二个选择框进行选择后，与选择值关联的一些选项出现在第六个列表框里，依次类推……
这个UI的逻辑就比较复杂，但使用了AJAX使得我们实现起来就简单多了，这个例子我们除了使用Action类，还要用到POJO类和Business类，然后我们扩展的话，可以通过Business类和数据库连接起来。
我们还是先看配置文件：
<action type="com.ajax.SelectAction"
scope="request" path="/ajax/select">
<forward name="success" path="/select.jsp"/>
</action>

然后看看Action类：
/*
/**
* Title : Base Dict Class
* Description : here Description is the function of class,here maybe multirows
* Copyright: Copyright (c) 2004
* @company Freeborders Co.,Ltd.
* @Goal Feng
* @Version 1.0
*/

package com.ajax;

import java.io.PrintWriter;
import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;

/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class SelectAction extends Action
{
public final ActionForward execute(ActionMapping mapping,
HttpServletResponse response)
throws Exception
{
response.setContentType("text/xml");
response.setHeader("Cache-Control","no-cache");
String type = request.getParameter("type");
String id = request.getParameter("id");
System.out.println(id);
StringBuffer sb=new StringBuffer("<select>");
sb.append("<type>"+type+"</type>");

List list = new SelectBusiness().getData(id);
for(int i=0;i<list.size();i++)
{
SelectForm sel = (SelectForm)list.get(i);
sb.append("<text>"+sel.getText()+"</text><value>"+sel.getValue()+"</value>");
}

sb.append("</select>");
PrintWriter out=response.getWriter();
out.write(sb.toString());
out.close();
System.out.println(sb.toString());
return mapping.findForward("success");
}
public static void main(String[] args)
{
}
}

POJO类和Business类：
package com.ajax;
/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class SelectForm
{
private String text;
private String value;

/**
* @return Returns the text.
*/
public String getText()
{
return text;
}
/**
* @param text The text to set.
*/
public void setText(String text)
{
this.text = text;
}
/**
* @return Returns the value.
*/
public String getValue()
{
return value;
}
/**
* @param value The value to set.
*/
public void setValue(String value)
{
this.value = value;
}
public static void main(String[] args)
{
}
}

package com.ajax;

import java.util.ArrayList;
import java.util.List;

/**
* @author Administrator
*
* TODO To change the template for this generated type comment go to
* Window - Preferences - Java - Code Style - Code Templates
*/
public class SelectBusiness
{
public List getData(String id)
{
ArrayList list = new ArrayList();
for(int i=1;i<6;i++)
{
SelectForm form = new SelectForm();
form.setText(id+i);
form.setValue(id+i);
list.add(form);
}
return list;
}

public static void main(String[] args)
{
}
}

最后是JSP文件：
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<TITLE>FB</TITLE>
<LINK href="images/magazin.css" type=text/css rel=stylesheet>
<LINK href="images/briefing.css" type=text/css rel=stylesheet>
<Meta http-equiv=Content-Type content="text/html; charset=utf-8">
<Meta content="MSHTML 6.00.2800.1498" name=GENERATOR>
<style type="text/css">

</style>
<script language="javascript">
function Add()
{
if(document.all.Education2.style.display=='block')document.all.Education2.style.display='none';
else document.all.Education2.style.display='block';
}
</script>
</HEAD>
<BODY leftMargin=0 topMargin=0 marginheight="0" marginwidth="0">
<script type="text/javascript" src="images/head.js"></script>
<script language=javascript>

function getResult(type,id) {
var url = "ajax/select.do?type="+type+"&id="+id;
if (window.XMLHttpRequest) {
req = new XMLHttpRequest();
}else if (window.ActiveXObject) {
req = new ActiveXObject("Microsoft.XMLHTTP");
}
if(req){
req.open("GET",true);
req.onreadystatechange = complete;
req.send(null);
}
}
function complete(){
if (req.readyState == 4) {
if (req.status == 200) {
var type = req.responseXML.getElementsByTagName("type");
var value = req.responseXML.getElementsByTagName("value");
var str=new Array();
for(var i=0;i<value.length;i++){
str[i]=value[i].firstChild.data;
}
var type = type[0].firstChild.data;

removeType1(type);

if(type=="0")
{

buildSelect(str,document.getElementById("select28"));
}
else if(type=="1")
{
buildSelect(str,document.getElementById("select32"));
}
else if(type=="2")
{
buildSelect(str,document.getElementById("select34"));
}

}
}
}
function buildSelect(str,str[i])
}
}

function removeType1(type)
{
var form = document.forms[0];
if(type=="0")
{
removeAll(form.select28);
removeAll(form.select29);
removeAll(form.select30);
removeAll(form.select31);
removeAll(form.select32);
removeAll(form.select33);
removeAll(form.select34);
removeAll(form.select35);
}
else if(type=="1")
{
removeAll(form.select31);
removeAll(form.select32);
removeAll(form.select33);
removeAll(form.select34);
removeAll(form.select35);
}
else if(type=="2")
{
removeAll(form.select34);
removeAll(form.select35);
}
else if(type=="3")
{

}
}

function selChange(f,h)
{
for(i = 0;i < f.length; i++)
{
if(f.options[i].selected == true)
{
h.options.add(new Option( f.options[i].text,f.options[i].value));
f.options.remove(i);
i--;
}
}
}

function removeAll(obj)
{
for(i=0;i<obj.length;i++)
{
obj.options.remove(i);
i--;
}
}

function addAll(f,h)
{
for(i = 0;i < f.length; i++)
{
h.options.add(new Option( f.options[i].text,f.options[i].value));
f.options.remove(i);
i--;
}
}

function changeSel(offer,getter,type)
{
removeType(type);
for(i=0;i<getter.length;i++)
{
getter.options.remove(i);
i--;
}
getter.options.add(new Option("",""));
for(i = 0;i < offer.length; i++)
{
getter.options.add(new Option(offer.options[i].text,offer.options[i].value));
}
}

function removeType(type)
{
var form = document.forms[0];
if(type=="0")
{
removeAll(form.select25);
removeAll(form.select28);
removeAll(form.select29);
removeAll(form.select30);
removeAll(form.select31);
removeAll(form.select32);
removeAll(form.select33);
removeAll(form.select34);
removeAll(form.select35);
}
else if(type=="1")
{
removeAll(form.select30);
removeAll(form.select31);
removeAll(form.select32);
removeAll(form.select33);
removeAll(form.select34);
removeAll(form.select35);
}
else if(type=="2")
{
removeAll(form.select31);
removeAll(form.select34);
removeAll(form.select35);
}
else if(type=="3")
{

}
}
function removeAll(obj)
{
for(i=0;i<obj.length;i++)
{
obj.options.remove(i);
i--;
}
}

</script>
<form>
<font face="Arial,Helvetica,sans-serif"></font>
<TABLE cellSpacing=0 cellPadding=0 width="100%" border=0>
<TBODY>
<TR>
<TD align=middle vAlign=top bgcolor="#eeeeee">
<TABLE cellSpacing=0 cellPadding=0 width=945 align=center
background=images/bg2.gif border=0>
<TBODY>
<TR>
<TD vAlign=top> <TABLE cellSpacing=0 cellPadding=0 width="95%" align=center border=0>
<TBODY>
<TR>
<TD width="97%" align=right> <p align="left"> Resource Management >> New
Staff</TD>
</TR>
<TR height=4>
<TD></TD>
</TR>
<TR>
<TD valign="top"> <table class=homeBody cellspacing=0 cellpadding=0 width="100%"
align=center border=0>
<tbody>
<tr>
<td height=25 colspan="2" nowrap><table class=grid style="WIDTH: 100%;" cellspacing=0 cellpadding=3>
<tbody>
<tr class=gridHeader>
<td width="26%" align=left bgcolor="#eeeeee" ><strong> Personal
Information</strong></td>
<td width="74%" align=left bgcolor="#eeeeee" ><span class="gridAlternating">Last
Modified : 06/06/2005</span></td>
</tr>
</tbody>
</table></td>
</tr>
<tr>
<td valign=middle nowrap><div align="right"><input style="width:50px" class="button" type="button" value="Save"
name="B323252">  <input style="width:50px" class="button" type="button" value="Undo" name="B323262">
</div></td>
</tr>
<tr>
<td colspan=2 valign="top" class="modifiedRow modifiedProducts">
<table id=DynamicTabsTable cellspacing=0 cellpadding=0
border=0 name="DynamicTabsTable">
<tbody>
<tr id=DynamicTabsTR>
<script language=JavaScript
src="images/Public.js"></script>
</tr>
</tbody>
</table>
<table width="100%" border="0" cellpadding="0" cellspacing="3" bordercolorlight="#C0C0C0" bordercolordark="#FFFFFF">

<tr>
<td nowrap><fieldset align="left" style="PADDING-RIGHT: 8px; PADDING-LEFT: 8px; PADDING-BOTTOM: 8px; LINE-HEIGHT: 30px; PADDING-TOP: 8px;width:900px">
<legend class=legend>Freeborders Experience</legend>
<table width="100%" height="15" border="0" align="center" cellspacing="0" bordercolorlight="#C0C0C0" bordercolordark="#FFFFFF" id="table21">
<tr>
<td nowrap><strong>FB Vertical Experience</strong></td>
<td colspan="2"><strong>FB Customer
Experience </strong></td>
</tr>
<tr>
<td height="26" valign="top" nowrap> </td>
<td colspan="2" valign="top" nowrap><strong>
<select name="select25" id="select25" style="WIDTH: 179px" onchange="getResult('0',document.forms[0].select25.value);">
<option value="b">b</option>
<option value="c">c</option>
</select>
</strong></td>
</tr>
<tr>
<td height="26" valign="top" nowrap>
<table border="0" cellspacing="0" cellpadding="0" id="table34">
<tr>
<td> <select id="select26" style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4" name="select26">
<option value="a">a</option>
</select>
</td>
<td width="50" align="middle" valign="middle" bordercolorlight="#C0C0C0" bordercolordark="#FFFFFF" class="tableblackborder"><div align="center">
<table width="80%" height="110" border="0" align="center" cellpadding="0" cellspacing="0" id="table35">
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button29" style="WIDTH: 30px" value=">" onclick="selChange(document.forms[0].select26,document.forms[0].select27);changeSel(document.forms[0].select27,document.forms[0].select25,'0')" />
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button30" style="WIDTH: 30px" value=">>" causesvalidation="False" onclick="addAll(document.forms[0].select26,'0')"/>
</div></td>
</tr>
<tr>
<td height="5"><div align="center"></div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button31" style="WIDTH: 30px" value="<" causesvalidation="False" onclick="selChange(document.forms[0].select27,document.forms[0].select26,1);changeSel(document.forms[0].select27,'0')"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button32" style="WIDTH: 30px" value="<<" causesvalidation="False" onclick="addAll(document.forms[0].select27,document.forms[0].select26);changeSel(document.forms[0].select27,'0')"/>
</div></td>
</tr>
</table>
</div></td>
<td> </td>
<td align="right"> <select id="select27"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select27">
<option value="b">b</option>
<option value="c" selected>c</option>
</select></td>
</tr>
</table></td>
<td colspan="2" valign="top" nowrap>
<table border="0" cellspacing="0" cellpadding="0" id="table36">
<tr>
<td> <select id="select28"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select28">
<option value="b1">b1</option>
</select></td>
<td width="50" align="middle" valign="middle" bordercolorlight="#C0C0C0" bordercolordark="#FFFFFF" class="tableblackborder"><div align="center">
<table width="80%" height="110" border="0" align="center" cellpadding="0" cellspacing="0" id="table37">
<tr>
<td><div align="center">
<input type="button" name="button2" id="button33" style="WIDTH: 30px" value=">" onclick="selChange(document.forms[0].select28,document.forms[0].select29);changeSel(document.forms[0].select29,document.forms[0].select30,'1')"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button34" style="WIDTH: 30px" value=">>" causesvalidation="False" onclick="addAll(document.forms[0].select28,'1')"/>
</div></td>
</tr>
<tr>
<td height="5"><div align="center"></div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button35" style="WIDTH: 30px" value="<" causesvalidation="False" onclick="selChange(document.forms[0].select29,document.forms[0].select28);changeSel(document.forms[0].select29,'1')"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button36" style="WIDTH: 30px" value="<<" causesvalidation="False" onclick="addAll(document.forms[0].select29,'1')"/>
</div></td>
</tr>
</table>
</div></td>
<td> </td>
<td> <select id="select29"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select29">
<option value="b2">b2</option>
</select></td>
</tr>
</table></td>
</tr>
<tr>
<td height="10" colspan="2" nowrap></td>
<td width="275" valign="top"> </td>
</tr>
<tr>
<td nowrap><strong>Project Experience</strong></td>
<td colspan="2" nowrap><strong>SubProject
Experience</strong></td>
</tr>
<tr>
<td height="10" valign="top" nowrap><strong>
<select name="select30" id="select30" style="WIDTH: 179px" onchange="getResult('1',document.forms[0].select30.value);">
<option value=""></option>
<option value="b2">b2</option>
</select>
</strong></td>
<td colspan="2" valign="top" nowrap><strong>
<select name="select31" id="select31" style="WIDTH: 179px" onchange="getResult('2',document.forms[0].select31.value);">
<option> </option>
<option value="b13">b13</option>
<option value="b14">b14</option>
</select>
</strong></td>
</tr>
<tr>
<td height="10" valign="top" nowrap>
<table border="0" cellspacing="0" cellpadding="0" id="table38">
<tr>
<td> <select id="select32"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select32">
<option value="b11">b11</option>
<option value="b12">b12</option>
</select></td>
<td width="50" align="middle" valign="middle" bordercolorlight="#C0C0C0" bordercolordark="#FFFFFF" class="tableblackborder"><div align="center">
<table width="80%" height="110" border="0" align="center" cellpadding="0" cellspacing="0" id="table39">
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button37" style="WIDTH: 30px" value=">" onclick="selChange(document.forms[0].select32,document.forms[0].select33);changeSel(document.forms[0].select33,document.forms[0].select31,'2')"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button38" style="WIDTH: 30px" value=">>" causesvalidation="False" onclick="addAll(document.forms[0].select32,'2')"/>
</div></td>
</tr>
<tr>
<td height="5"><div align="center"></div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button39" style="WIDTH: 30px" value="<" causesvalidation="False" onclick="selChange(document.forms[0].select33,document.forms[0].select32);changeSel(document.forms[0].select33,'2')"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button40" style="WIDTH: 30px" value="<<" causesvalidation="False" onclick="addAll(document.forms[0].select33,'2')"/>
</div></td>
</tr>
</table>
</div></td>
<td> </td>
<td> <select id="select33"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select33">
<option value="b13">b13</option>
<option value="b14">b14</option>
</select></td>
</tr>
</table></td>
<td colspan="2" valign="top" nowrap>
<table border="0" cellspacing="0" cellpadding="0" id="table40">
<tr>
<td> <select id="select34"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select34">
<option value="b111">b111</option>
<option value="b112">b112</option>
<option value="b113">b113</option>
</select></td>
<td width="50" align="middle" valign="middle" bordercolorlight="#C0C0C0" bordercolordark="#FFFFFF" class="tableblackborder"><div align="center">
<table width="80%" height="110" border="0" align="center" cellpadding="0" cellspacing="0" id="table41">
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button41" style="WIDTH: 30px" value=">" onclick="selChange(document.forms[0].select34,document.forms[0].select35);"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button42" style="WIDTH: 30px" value=">>" causesvalidation="False" onclick="addAll(document.forms[0].select34,document.forms[0].select35)"/>
</div></td>
</tr>
<tr>
<td height="5"><div align="center"></div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button43" style="WIDTH: 30px" value="<" causesvalidation="False" onclick="selChange(document.forms[0].select35,document.forms[0].select34);"/>
</div></td>
</tr>
<tr>
<td><div align="center">
<input name="button2" type="button" class="button" id="button44" style="WIDTH: 30px" value="<<" causesvalidation="False" onclick="addAll(document.forms[0].select35,document.forms[0].select34)"/>
</div></td>
</tr>
</table>
</div></td>
<td> </td>
<td> <select id="select35"
style="WIDTH: 180px; HEIGHT: 120px" multiple="multiple" size="4"
name="select35">
<option value="b114">b114</option>
<option value="b115">b115</option>
<option value="b116">b116</option>
</select></td>
</tr>
</table></td>
</tr>

</table></td>
</tr>
</table>
</fieldset></td>
</tr>
</table></td>
</tr>
</tbody>
</table></TD>
</TR>
</TBODY>
</TABLE>
<TABLE cellSpacing=0 cellPadding=0 width="95%" align=center border=0>
<TBODY>
<TR valign="top">
<TD width="97%" align="left" valign="middle"><div align="right"><input style="width:50px" class="button" type="button" value="Save"
name="B32">  <input style="width:50px" class="button" type="button" value="Undo" name="B3">
</div></TD>
</TR>
</TBODY>
</TABLE>

</TD>
</TR>
</TBODY>
</TABLE>
<script type="text/javascript" src="images/bottom.js"></script></TD></TR></TBODY></TABLE>
</BODY></form></HTML>

虽然这个JSP复杂多了，但是关于AJAX的代码还是跟前面的例子一样，在这里我也就不多说了，请大家自己看。

六、蛇足

好了，例子都说完了。废话也就不多说了，只说一件事：AJAX好像来势汹汹，要把我们用得极其普遍、极其习惯的Struts等的MVC开发模式取代掉一样。其实，AJAX有它的优点，同样也有它的缺点。它一般用在用户不想等待返回结果的时候和复杂的UI上；其他时候，我们还是可以使用Struts等常规方法。一句话，不要为了使用AJAX而使用AJAX，而是要在适合于使用AJAX的地方使用AJAX。注：本文参考了一些网友的作品，不好列出参考文献，在此对他们的工作表示感谢！

AJAX实例入门

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