本篇文章主要是对AJAX级联下拉框的简单实现案例进行了介绍，需要的朋友可以过来参考下，希望对大家有所帮助
需要的JAVA类代码如下:package com.ajaxlab.ajax;import java.util.ArrayList;import java.util.Collection;import java.util.Iterator;import org.jdom.document;import org.jdom.Element;import org.jdom.input.SAXBuilder;import com.ajaxlab.ajax.ProductClass;public class ClassService { private document dom; public ClassService(){ try{ SAXBuilder builder=new SAXBuilder(); this.dom=builder.build(ClassService.class.getResource("product.xml")); }catch(Exception e){ e.printStackTrace(); } } public ProductClass[] getAllClass1(){ Collection products=new ArrayList(); Iterator iterator=this.dom.getRootElement().getChildren().iterator(); do{ Element element=(Element)iterator.next(); ProductClass product=new ProductClass(element.getAttributevalue("id"), element.getAttributevalue("className")); products.add(product); }while(iterator.hasNext()); return (ProductClass[])products.toArray(new ProductClass[0]); } public ProductClass[] getAllClass2ById(String class1Id){ Collection products=new ArrayList(); Element classElement=null; Iterator iterator=this.dom.getRootElement().getChildren().iterator(); do{ Element element=(Element)iterator.next(); if(class1Id.equalsIgnoreCase(element.getAttributevalue("id"))){ classElement=element; break; } }while(iterator.hasNext()); if(classElement!=null){ Iterator iter=classElement.getChildren().iterator(); do{ Element element=(Element)iter.next(); ProductClass product=new ProductClass(element.getAttributevalue("id"),element.getAttributevalue("className")); products.add(product); }while(iter.hasNext()); return (ProductClass[])products.toArray(new ProductClass[0]); } else{ return null; } } public ProductClass[] getAllClass3ById(String class1Id,String class2Id) { Collection products = new ArrayList(); Element class1Element = null; Element class2Element = null; Iterator iterator = this.dom.getRootElement().getChildren().iterator(); do { Element element = (Element)iterator.next(); if(class1Id.equalsIgnoreCase(element.getAttributevalue("id"))) { class1Element = element; break; } }while(iterator.hasNext()); if(class1Element!=null) { Iterator iter = class1Element.getChildren().iterator(); do { Element element = (Element)iter.next(); if(class2Id.equalsIgnoreCase(element.getAttributevalue("id"))) { class2Element = element; break; } }while(iter.hasNext()); if(class2Element!=null) { Iterator iter2 = class2Element.getChildren().iterator(); do { Element element = (Element)iter2.next(); ProductClass product = new ProductClass(element.getAttributevalue("id"),element.getAttributevalue("className")); products.add(product); }while(iter2.hasNext()); } return (ProductClass[])products.toArray(new ProductClass[0]); } else return null;}}<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE class SYSTEM "product.dtd" ><class> <class1 className="电脑配件" id="1"> <class2 className="内存" id="1"> <class3 id="1" className="kingmax"></class3> <class3 id="2" className="kingston"></class3> <class3 id="3" className="samsung"></class3> <class3 id="4" className="hydadi"></class3> <class3 id="5" className="ibm"></class3> </class2> <class2 className="硬盘" id="2"> <class3 id="6" className="hithait"></class3> <class3 id="7" className="IBM"></class3> <class3 id="8" className="samsung"></class3> <class3 id="9" className="westdata"></class3> </class2> </class1> <class1 className="食品配件" id="2"> <class2 className="汉堡包" id="1"> <class3 id="1" className="麦当劳"></class3> <class3 id="2" className="肯得基"></class3> <class3 id="3" className="罗杰丝"></class3> </class2> <class2 className="饮料" id="2"> <class3 id="4" className="cocacola"></class3> <class3 id="5" className="sprite"></class3> <class3 id="6" className="coffee"></class3> <class3 id="7" className="water"></class3> </class2> </class1></class><?xml version="1.0" encoding="GB2312" ?><!ELEMENT class (class1+)><!ELEMENT class1 (class2+)><!ATTLIST class1 className NMTOKEN #REQUIRED><!ATTLIST class1 id NMTOKEN #REQUIRED><!ELEMENT class2 (class3+)><!ATTLIST class2 className NMTOKEN #REQUIRED><!ATTLIST class2 id NMTOKEN #REQUIRED><!ELEMENT class3 EMPTY><!ATTLIST class3 className NMTOKEN #REQUIRED><!ATTLIST class3 id NMTOKEN #REQUIRED>JSP:(1)getClass.jsp 充当业务层供ajax调用<%@ page contentType="text/html; charset=gb2312"%><%@ page import="com.ajaxlab.ajax.*"%><%String class1Id = request.getParameter("class1Id");String class2Id = request.getParameter("class2Id");if("".equals(class1Id)) class1Id = null;if("".equals(class2Id)) class2Id = null;ClassService service = new ClassService();if((class1Id!=null)&&(class2Id==null)) {ProductClass[] classes = service.getAllClass2ById(class1Id);if(classes!=null) { for(int i=0;i<classes.length;i++) { out.print(classes[i].getId()+","+classes[i].getClassName()+"|"); }}}else if((class1Id!=null)&&(class1Id!=null)) {ProductClass[] classes = service.getAllClass3ById(class1Id,class2Id);if(classes!=null) { for(int i=0;i<classes.length;i++) { out.print(classes[i].getId()+","+classes[i].getClassName()+"|"); }}}%>(2)divmenu.jsp<%@ page contentType="text/html; charset=gb2312"%><%@ page import="com.ajaxlab.ajax.*"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><script type="text/javascript" src=http://www.shancun.net/skin/default/image/nopic.gif ></script><script type="text/javascript">function doChange() {var f = document.forms[0];send_request("GET","getClass.jsp?class1Id="+f.select11.value+"&class2Id=",null,"TEXT",populateClass2);}function doChange2() {var f = document.forms[0];send_request("GET","getClass.jsp?class1Id="+f.select11.value+"&class2Id="+f.select12.value,null,"TEXT",populateClass3);}function populateClass2(){ var f=document.forms[0]; if(http_request.readystate==4){ if(http_request.status==200){ var list=http_request.responseText; var classList=list.split("|"); f.select12.options.length=1; for(var i=0;i<classList.length-1;i++){ var temp=Trim(classList[i]).split(","); f.select12.add(new Option(temp[1],temp[0])); } } }} function populateClass3(){ var f=document.forms[0]; if(http_request.readystate==4){ if(http_request.status==200){ var list=http_request.responseText; var classList=list.split("|"); f.select13.options.length=1; for(var i=0;i<classList.length-1;i++){ var temp=Trim(classList[i]).split(","); f.select13.add(new Option(temp[1],temp[0])); } } } } function LTrim(str){ var whitespace = new String(" /t/n/r"); var s = new String(str); if (whitespace.indexOf(s.charAt(0)) != -1) { var j=0, i = s.length; while (j < i && whitespace.indexOf(s.charAt(j)) != -1) { j++; } s = s.substring(j, i); } return s;}function RTrim(str){ var whitespace = new String(" /t/n/r"); var s = new String(str); if (whitespace.indexOf(s.charAt(s.length-1)) != -1) { var i = s.length - 1; while (i >= 0 && whitespace.indexOf(s.charAt(i)) != -1) { i--; } s = s.substring(0, i+1); } return s;}function Trim(str){ return RTrim(LTrim(str));}</script><% ClassService service = new ClassService(); ProductClass[] classes = service.getAllClass1();%><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Insert title here</title></head><body><center><form name="classForm" method="post" action=""><select name="select11" id="select11" onchange="doChange(this.value)"><option value="">请选择分类一</option><%for(int i=0;i<classes.length;i++) { out.println("<option value='"+classes[i].getId()+"'>"+classes[i].getClassName()+"</option>");}%></select><select name="select12" id="select12" onchange="doChange2(this.value)"><option value="">请选择分类二</option></select><select name="select13" id="select13"><option value="">请选择分类三</option></select></form></center></body></html>
