jsp实现将信息放入xml中的方法

省： <select id="province" name="province" onchange="jssubmit()"> 
    <option value="北京" selected="selected">北京</option> 
    <option value="广东">广东</option> 
    <option value="海南">海南</option> 
  </select> 
市： <select id="city" name="city"> 
    <option value="北京">北京</option> 
 </select>

function jssubmit() { 
  createxmlhttprequest(); 
     var province = document.getelementbyid("province"); 
  //解决客户端向服务器端传输中文乱码 
     var uri = "ajaxaction?value=" + encodeuri(encodeuri(province.value)); 
  xmlhttp.open("post", uri, true); 
  xmlhttp.setrequestheader("content-type","application/x-www-form-urlencoded;") 
  xmlhttp.onreadystatechange = processresponse;//回调函数啊！ 
  xmlhttp.send(null); 
}

public class ajaxaction extends httpservlet { 
 private static final long serialversionuid = 1l; 
 private static map<string, string[]> map = new hashmap<string, string[]>(); 
 static { 
  string[] cities1 = { "海口", "琼海", "三亚" }; 
  string[] cities2 = { "广州", "珠海", "佛山", "深圳" }; 
  string[] cities3 = { "北京" }; 
  map.put("北京", cities3); 
  map.put("广东", cities2); 
  map.put("海南", cities1); 
 } 
st方法{ 
  string province = request.getparameter("value");// 解决客户端向服务器端传输中文乱码 
  string provicecn = urldecoder.decode(province, "utf-8"); 
  string[] cities = map.get(provicecn);//根据传来的省，查出已经存放进map中对应的市 
  response.setcontenttype("text/xml; charset=utf-8"); 
  stringbuffer buff=new stringbuffer("<citylist>");///准备拼字符串...... 
   for (string city : cities) 
    { 
     buff.append("<city>").append(city) .append("</city>"); 
    } 
  buff.append("</citylist>"); 
  response.getwriter().println(buff.tostring());

function processresponse() { 
  if(xmlhttp.readystate == 4) { 
   if(xmlhttp.status == 200) { 
    var cities = xmlhttp.responsexml.getelementsbytagname("city"); 
    var displayselect = document.getelementbyid("city"); 
    displayselect.innerhtml = null; 
    for (var i= 0 ;i < cities.length ; i++){    
     if (i == 0) {       
     var a= xmlhttp.responsexml.getelementsbytagname("city")[i].firstchild.data;//用firstchild方法，其他方法我用text方法不管用~不知道怎么回事 
      var op = new option(a, a, true, true); 
     } else { 
      var a= xmlhttp.responsexml.getelementsbytagname("city")[i].firstchild.data; 
      var op = new option(a, a); 
      alert(a); 
     } 
     displayselect.options[i] = op; 
    }     
   } else { 
    window.alert("请求的页面有异常"); 
   } 
 } 
}