Ajax实现三级联动下拉框

<% @ page contentType  =   " text/html; charset=GBK "    import = " java.util.*,com.wehave.hyerp.procurement.domain.Cgsqd " %>
<% @ taglib uri = " struts-html "  prefix = " html "   %>
<% @ taglib uri = " struts-logic "  prefix = " logic "   %>
<% @ taglib uri = " struts-bean "  prefix = " bean "   %>
< html >
     < head >
         < title >   </ title >
         < link rel  =   " stylesheet "  type  =   " text/css "  href  =   " ../css/olstyle.css " >     
         < SCRIPT type = " text/javascript " >
        var req;
        window.onload = function() {
        }
        
        function Change_Select()
         {
            var zhi=document.getElementById('m_gykfwzlbb_lbbm').value;
            var url="sqdSelect.go?method=getSkill&id="+zhi;
            if(zhi=="0"){
                alert("请选择您要察看的信息");
                   return;
            }else{
                if(window.XMLHttpRequest)
                {
                    req=new XMLHttpRequest();
                }else if(window.ActiveXObject)
                {
                    req=new ActiveXObject("Microsoft.XMLHTTP");
                }
                
                if(req)
                {
                    req.open("GET",url,true);
                    req.onreadystatechange=callback;
                    req.send(null);
                }
            }
        }
        
        function Change_Select2()
         {
            var zhi=document.getElementById('m_lbbm_se').value;
            //alert(zhi.substring(0,2));
            if(zhi=="0"){
                alert("请选择您要察看的信息");
                   return;
               }
            if(zhi.substring(0,2)=="WY"){
                var url="sqdSelect.go?method=getSkill2&id="+zhi;
                if(window.XMLHttpRequest)
                {
                    req=new XMLHttpRequest();
                }else if(window.ActiveXObject)
                {
                    req=new ActiveXObject("Microsoft.XMLHTTP");
                }
                
                if(req)
                {
                    req.open("GET",url,true);
                    req.onreadystatechange=callback2;
                    req.send(null);
                }
            }else{
                parent.topFram.location ="sqdSelectAll.go?method=getlistAll&id="+zhi;
            }
        }
        
        function Change_Select3()
         {
            var zhi=document.getElementById('m_lbbm_th').value;
            //alert(zhi.substring(0,2));
            if(zhi=="0"){
                alert("请选择您要察看的信息");
                   return;
               }else{
                parent.topFram.location ="sqdSelectAll.go?method=getlistAll2&id="+zhi;
            }
        }
        
        function callback()
         {
            if(req.readyState == 4)
            {
                if(req.status == 200)
                {
                    parseMessage();
                }else{
                    alert("Not able to retrieve description"+req.statusText);
                }
            }
        }
        
        function callback2()
         {
            if(req.readyState == 4)
            {
                if(req.status == 200)
                {
                    parseMessage2();
                }else{
                    alert("Not able to retrieve description"+req.statusText);
                }
            }
        }
        
        function parseMessage()
         {
            var xmlDoc=req.responseXML.documentElement;
            var xSel=xmlDoc.getElementsByTagName('select');
            var select_root=document.getElementById('m_lbbm_se');
            select_root.options.length=0;
            
            for(var i=0;i<xSel.length;i++)
            {
                var xValue=xSel[i].childNodes[0].firstChild.nodeValue;
                var xText=xSel[i].childNodes[1].firstChild.nodeValue;
                var option=new Option(xText,xValue);
                try{
                    select_root.add(option);
                }catch(e){
                }
            }
        }
        
        function parseMessage2()
         {
            var xmlDoc=req.responseXML.documentElement;
            var xSel=xmlDoc.getElementsByTagName('select');
            var select_root=document.getElementById('m_lbbm_th');
            select_root.options.length=0;
            
            for(var i=0;i<xSel.length;i++)
            {
                var xValue=xSel[i].childNodes[0].firstChild.nodeValue;
                var xText=xSel[i].childNodes[1].firstChild.nodeValue;
                var option=new Option(xText,xValue);
                try{
                    select_root.add(option);
                }catch(e){
                }
            }
        }
        
        
        
     </ SCRIPT >
     </ head >

< body bgcolor  =   " #C8D0D4 " >
     < html:form action = " /cgsqdNewAction.go " >  
     < TABLE  class   =   " cbToolbar "  id  =   " idToolbar "  cellpadding  =   ' 0 '  cellspacing  =   ' 0 ' >
         < TR align  =   " left "  valign  =   " top "   >
             < TD  NOWRAP >& nbsp;物质类别: & nbsp; & nbsp;
                 < html:select property = " m_gykfwzlbb_lbbm "  onchange = " Change_Select() " >
                     < html:option value = " 0 " > 请选择 </ html:option >
                        < html:options collection = " LbfList "  property = " m_gykfwzlbb_lbbm "  labelProperty = " m_gykfwzlbb_lbmc " />
                 </ html:select >   & nbsp;
                 < html:select property = " m_lbbm_se "  styleId = " m_lbbm_se "  onchange = " Change_Select2() " >
                     < html:option value = " 0 " >& nbsp; & nbsp; & nbsp; </ html:option >
                 </ html:select >
                 < html:select property = " m_lbbm_th "  styleId = " m_lbbm_th "  onchange = " Change_Select3() " >
                     < html:option value = " 0 " >& nbsp; & nbsp; & nbsp; </ html:option >
                 </ html:select >
                
             </ TD >
            
         </ tr >
     </ table >
      </ html:form >
</ body >
</ html >

action中的代码：
/** *//**
     * 
     * 查询物质编码类别列表操作(一级)
     * */
    public ActionForward doSelectWzlb(
            ActionMapping mapping,
            ActionForm form,
            HttpServletRequest req,
            HttpServletResponse res) {
        HttpSession session = req.getSession();
        UserSession userSession =
            (UserSession) session.getAttribute("userSession");
        permission.setUserID(userSession.getUserId());
        permission.setUserName(userSession.getUserName());
        permission.setModuleName("m_cgsqd");
        permission.setActionStr("'m_select'");
        if(permissionService.checkUserPermission(permission)){
            int updateSign=0;
            try{
                cgsqdService.updateCgsqwzhzb_sqsl();
                updateSign=1;
            }catch(Exception e){
                e.printStackTrace();
                updateSign=0;
            }
            if(updateSign==1){
                List LbfList=cgsqdService.treeListWzlb2();
                req.setAttribute("LbfList",LbfList);
                return mapping.findForward("tools");
            }else{
                return null;
            }
        }else{
            return mapping.findForward("failure");
        }
    }
    
    /** *//**
     * 
     * 查询物质编码类别列表操作(二级)
     * */
    public ActionForward doSelectWzlb1(
            ActionMapping mapping,
            ActionForm form,
            HttpServletRequest req,
            HttpServletResponse res) {
        HttpSession session = req.getSession();
        UserSession userSession =
            (UserSession) session.getAttribute("userSession");
        permission.setUserID(userSession.getUserId());
        permission.setUserName(userSession.getUserName());
        permission.setModuleName("m_cgsqd");
        permission.setActionStr("'m_select'");
        if(permissionService.checkUserPermission(permission)){
            int updateSign=0;
            try{
                cgsqdService.updateCgsqwzhzb_sqsl();
                updateSign=1;
            }catch(Exception e){
                e.printStackTrace();
                updateSign=0;
            }
            if(updateSign==1){
                List LbfList=cgsqdService.treeListWzlb2();
                req.setAttribute("LbfList",LbfList);
                return mapping.findForward("tools1");
            }else{
                return null;
            }
        }else{
            return mapping.findForward("failure");
        }
    }
    
    /** *//**
     * 
     * 查询物质编码类别列表操作(三级)
     * */
    public ActionForward getSkill(
            ActionMapping mapping,
            ActionForm form,
            HttpServletRequest req,
            HttpServletResponse res) {
        HttpSession session = req.getSession();
        UserSession userSession =
            (UserSession) session.getAttribute("userSession");
        permission.setUserID(userSession.getUserId());
        permission.setUserName(userSession.getUserName());
        permission.setModuleName("m_cgsqd");
        permission.setActionStr("'m_select'");
        if(permissionService.checkUserPermission(permission)){
            String id=req.getParameter("id");
            
            res.setContentType("text/xml;charset=GBK");
            res.setHeader("Cache-Control","no-cache");
            String xml_start="<?xml version=/"1.0/" encoding=/"GBK/"?>";
            xml_start+="<selects>";
            String xml_end="</selects>";
            String xml="<select><value>0</value><text>请选择</text></select>";
            String m_lbbm_se="";
            String m_lbmc_se="";
            List LbfList=null;
            if(id.equals("WY")){
                LbfList=cgsqdService.treeListWzlb3_2(id);
            }else{
                LbfList=cgsqdService.treeListWzlb3_1(id);    
            }
            Iterator it=LbfList.iterator();
            while(it.hasNext()){
                Cgsqd cgsqd=(Cgsqd)it.next();
                m_lbbm_se=cgsqd.getM_gykfwzlbb_lbbm();
                m_lbmc_se=cgsqd.getM_gykfwzlbb_lbmc();
                xml +="<select><value>"+m_lbbm_se+"</value><text>"+m_lbmc_se+"</text></select>";
            }
            String last_xml=xml_start+xml+xml_end;
            logger.debug("XML是："+last_xml);
            try {
                res.getWriter().write(last_xml);
            } catch (IOException e) {
                e.printStackTrace();
            }
            return null;
        }else{
            return null;
        }
    }