AJAX二级下拉框联动

<SCRIPT type="text/javascript">
        var req;
        window.onload=function(){
        }
        
        function Change_Select(url, parentInputId, childInputId)
        {
            var parentInputValue = document.getElementById(parentInputId).value;
            var showUrl = url + "&parentInputId="+ parentInputId + "&parentInputValue=" + parentInputValue;
            //alert(showUrl);
            showUrl=encodeURI(showUrl); 
  			//alert(showUrl);
  			showUrl=encodeURI(showUrl);
            //alert(showUrl);
            if(window.XMLHttpRequest)
            {
                req=new XMLHttpRequest();
            }else if(window.ActiveXObject)
            {
                req=new ActiveXObject("Microsoft.XMLHTTP");
            }
            
            if(req)
            {
                req.open("GET",showUrl,true);
                req.onreadystatechange= function() {
                	callback(childInputId);
                }
                req.send(null);
            }
        }
        
        function callback(childInputId)
        {
            if(req.readyState == 4)
            {
                if(req.status == 200)
                {
                    parseMessage(childInputId);
                }else{
                	// Not able to retrieve descriptionInvalid URI: isHexDigit
                    alert("Not able to retrieve description"+req.statusText);
                }
            }
        }
        
        function parseMessage(childInputId)
        {
        	//alert();
            var xmlDoc=req.responseXML.documentElement;
            if(xmlDoc == 'null') {
            	alert("xmlDoc="+xmlDoc);
            }
            var xSel=xmlDoc.getElementsByTagName('select');
            var select_child=document.getElementById(childInputId);
            var select_child_length = select_child.options.length;
            for(var i = select_child_length-1; i >= 0; i--){
            	select_child.remove(i);
            }
            
            //alert("xSel.length="+xSel.length);
            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_child.options.add(option);
                }catch(e){
                }
            }
            
            
        }
</SCRIPT>

HTML调用：

<select id="parentId" onChange="Change_Select('seriesTextboxAction.do', 'parentId', 'childId')">
    <option value="">- Select One -</option>
    <option value="111">111</option>
    <option value="222">222</option>
</select>

<select id="childId">
    <option value="">- Select One -</option>
</select>

JAVA(Action)调用：

List<DropTo> dropList = Data List(from DB or other file);
int childListSize = dropList.size();
																response.setContentType("text/xml");						        response.setHeader("Cache-Control","no-cache");

StringBuffer buffer = new StringBuffer();
buffer.append("<selects>");
						        						        if(childListSize > 0) {
    for(int i = 0; i < childListSize; i ++) {
        DropTo dropFromDB = dropList.get(i);
        String showKey = dropFromDB.getShowKey();  
        String showValue = dropFromDB.getHiddenValue();
        System.out.println("showKey="+showKey+"  showValue="+showValue);
        buffer.append("<select><value>").append(showKey).append("</value>");
        buffer.append("<text>").append(showValue).append("</text></select>");
    }
    buffer.append("</selects>");
    response.getWriter().write(buffer.toString());
    response.getWriter().flush();
response.getWriter().close();						        
}

Struts:

<action name="seriesTextboxAction" class="xxxx.SeriesTextboxAction">
    <result name="success"></result>
</action>