二级联动基本代码

function createXMLHttpRequest() {   
            if (window.ActiveXObject) {   
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");   
            }   
            else if (window.XMLHttpRequest) {   
                xmlHttp = new XMLHttpRequest();                   
            }
            
        }   
// 删除城市选项    
function clearCityList(){    
    var citys = document.getElementById("city");    
    while(citys.childNodes.length > 0){    
        citys.removeChild(citys.childNodes[0]);    
    }    
}    
   
//选项省份时    
function selectProvince(){    
    var province = document.getElementById("province").value;//获取省份值    
        
    if(province == ""){ //如果为空,则清空城市选项    
        clearCityList();    
        var citySelect = document.getElementById("city"); //获取城市select组件    
        var option = document.createElement("option");    
        option.appendChild(document.createTextNode("请选择城市"));    
        citySelect.appendChild(option);    
        return ; //返回    
    }    
    //服务器处理地址,是一个Servlet    
    var url = encodeURI("ajax.portal?action=autoUpdate&province=" + province);
    url = encodeURI(url); 
    createXMLHttpRequest();//创建xmlHttp对象;    
    xmlHttp.onreadystatechange = handleStateChange; //回调函数    
    xmlHttp.open("GET",url,true);    
    xmlHttp.send(null);    
}    
   
//回调函数    
function handleStateChange(){    
    if(xmlHttp.readyState == 4){    
        if(xmlHttp.status == 200){    
            updateCitysList();    
        }    
    }    
}    
   
//页面更新城市集合函数    
function updateCitysList(){    
    clearCityList();//首先删除先前的城市选项    
    var citySelect = document.getElementById("city"); //获取城市select组件    
    var results = xmlHttp.responseXML.getElementsByTagName("city");//获取Ajax返回的结果,city为返回的XML里的节点    
    var option = null;    
    for(var i=0; i<results.length; i++){            
        option = document.createElement("option");    
        option.appendChild(document.createTextNode(results[i].firstChild.nodeValue));    
        citySelect.appendChild(option);    
    }    
} 


<logic:present name="provinces" scope="request">   
            <html:select property="province" styleId="province" onchange="selectProvince();">   
                <html:option value="">请选择省份</html:option>   
                <html:options name="provinces" labelName="provinces" />   
            </html:select>   
   
            <html:select property="city" styleId="city" style="width:90px">   
                <html:option value="">请选择城市</html:option>   
            </html:select>   
        </logic:present>       

if("autoUpdate".equals(form.getAction())){
			response.setContentType("text/xml; charset=UTF-8");//xml
	        response.setHeader("Cache-Control","no-cache");//HTTP1.1
	        response.setHeader("Pragma","no-cache");//HTTP1.0
	        response.setDateHeader("Expires",0);
	        PrintWriter out=null;
	        String name = request.getParameter("province");   
			try {
				out = response.getWriter();
//				name = new String(name.getBytes("ISO8859-1"), "UTF-8"); 
				name=java.net.URLDecoder.decode(name,"UTF-8");
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}   
	        System.out.println("name="+name);
	        Dom4jUtil dom=new Dom4jUtil();
			String fileName=getRealPath()+File.separator+"src"+File.separator+"city.xml";
			System.out.println("fileName="+fileName);
			dom.parse(fileName);
			StringBuffer sb = new StringBuffer("<citys>");
			List citys = dom.getChildList();//获取城市
			System.out.println("citys.size="+citys.size());
			for(int i=0;i<citys.size();i++){
				KeyValue city=(KeyValue)citys.get(i);
//				System.out.println("city.getKey()="+city.getKey());
				if(city.getKey().equals(name)){
					sb.append("<city>");    
					sb.append(city.getValue());    
					sb.append("</city>");
				}
			}
			sb.append("</citys>");    
	        System.out.println("sb.toString="+sb.toString());    
	        out.print(sb.toString());    
	        out.flush();    
	        out.close();    

		}