㈠ java二级联动，怎样在选了前面一个之后，后面的也跟着动
java中要实现二级联动，应该使用ajax技术，实例如下：
varreq;
functionchooseEmp()
{
varemp=document.getElementById('empId');
varurl="MagEmp?emp="+escape(emp.value);
if(window.XMLHttpRequest){
req=newXMLHttpRequest();
}elseif(window.ActiveXObject){
req=newActiveXObject("Microsoft.XMLHTTP");
}
if(req){
req.open("GET",url,true);
req.onreadystatechange=callback;
req.send(null);
}
}
functioncallback()
{
if(req.readyState==4)
{
if(req.status==200)
{
parseMessage();
}else{
alert("Notabletoretrievedescription"+req.statusText);
}
}
}
functionparseMessage()
{
varxmlDoc=req.responseXML.documentElement;
varxSel=xmlDoc.getElementsByTagName('select');
varselect_root=document.getElementById('magId');
select_root.options.length=0;
for(vari=0;i<xSel.length;i++)
{
varxValue=xSel[i].childNodes[0].firstChild.nodeValue;
varxText=xSel[i].childNodes[1].firstChild.nodeValue;
varoption=newOption(xText,xValue);
try{
select_root.add(option);
}catch(e){
}
}
}