初学Ajax

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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",url, 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,keyword2,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", url, 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,keyword2,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", url, 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, ActionForm form,
             HttpServletRequest request,
             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",url, 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,sel) {
         sel.options.length=0;
         for(var i=0;i<str.length;i++) {
                 sel.options[sel.options.length]=new Option(str[i],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,document.forms[0].select27);changeSel(document.forms[0].select27,document.forms[0].select25,'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,document.forms[0].select25,1);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="button32" style="WIDTH: 30px" value="<<" causesvalidation="False" onclick="addAll(document.forms[0].select27,document.forms[0].select26);changeSel(document.forms[0].select27,document.forms[0].select25,'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,document.forms[0].select29);changeSel(document.forms[0].select29,document.forms[0].select30,'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,document.forms[0].select30,'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,document.forms[0].select28);changeSel(document.forms[0].select29,document.forms[0].select30,'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,document.forms[0].select33);changeSel(document.forms[0].select33,document.forms[0].select31,'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,document.forms[0].select31,'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,document.forms[0].select32);changeSel(document.forms[0].select33,document.forms[0].select31,'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！