急~!!struts +ajax 级联菜单.问题~!盼各位大侠帮帮忙~!

[zhaochunhui]

request.responseXML.documentElement;返回null问题~!!!!
具体如下:
显示页面:
<SCRIPT type="text/javascript">
var req;
window.onload=function(){
}
function Change_Select()
{
var zhi=document.getElementById('province').value;
var url="/teach/aaa.do?method=g1&id="+zhi;
// alert(url);
if(zhi==""){
alert("请选择您要察看的信息");
return;
}else{
if(window.XMLHttpRequest)
{
req=new XMLHttpRequest();
}else if(window.ActiveXObject)
{ try{
req=new ActiveXObject("Microsoft.XMLHTTP");
}catch(e){
try{
}catch(e){
req=new ActiveXObject("Msxml2.XMLHTTP");
}
}
}
if(req)
{
req.open("GET",url,true);
req.onreadystatechange=callback;
req.send(null);
}
}
}
function callback()
{
if(req.readyState == 4)
{
if(req.status == 200)
{
var xmlDoc=req.responseXML.documentElement;
alert(xmlDoc);
parseMessage();
}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('city');
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){
}
}
}
<td height="29" width="30%">
<bean:message key="LoginForm.sheng"/>
<html:select property="province" onchange="Change_Select()">
<html:option value="">--</html:option>
<html:options collection="provinceid" property="value" labelProperty="label"/>
</html:select>
</td>
<td width="30%" id="mycity">

<html:select property="city">
<html:option value="">---</html:option>
</html:select>
</td>

[zhaochunhui]

具体的action 操作如下:
...
String method=req.getParameter("method");
//String id=rf.getId();
String id=req.getParameter("id");
//res.setContentType("text/xml;charset=UTF-8");
res.setHeader("Cache-Control","no-cache");
String strSQL="";
String xml_start="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";
xml_start+="<selects>";
String xml_end="</selects>";
String xml="<select><value>0</value><text>--</text></select>";
DBCPool dbc= new DBCPool();
Connection conn=dbc.getConnection("wy_manager");
Statement stmt=null;
if(conn!=null){
try{
stmt=conn.createStatement();
}catch(SQLException err){
System.out.println(err.getMessage());

}
}
if(method.equals("g1")){
strSQL="select cityID id,city name from city where father="+id;
}else if(method.equals("g1")){
strSQL="select areaID id,area name from area where father="+id;
}
ResultSet rs=null;

try{
rs=stmt.executeQuery(strSQL);
while(rs.next()){
xml +="<select><value>"+rs.getString("id")+"</value><text>"+rs.getString("name")+"</text></select>";
}
}catch(Exception e){
e.printStackTrace();
}
..

String last_xml=xml_start+xml+xml_end;
try {
res.getWriter().write(last_xml);

} catch (Exception e1) {
e1.printStackTrace();
}
--------------------------------------------------
我将数据存储在 response 中.在校检http_request.status==200,信息可以成功返回 不过在查看request.responseXML.documentElement 的时候 返回来的却是 null.
请各位大侠帮忙看看~!是什么原因~!
是不是 这句有问题:res.getWriter().write(last_xml);

请大侠们指点迷津~!

[zhaochunhui]

what 人呢 ? 人都去哪了 晕
555555555555555555555555555555555

[woaiwanghuan]

你可以跟踪调试啊,看看是不是last_xml是空的!

[tcmis]

学习，关注。

[zhaochunhui]

是说让我将last_xml打印出来吗？
不应该是空的吧~！

[zhaochunhui]

怎么没有人来呢~！各位大侠帮忙看看阿~！

[logonin]

mark!up!