How to dynamically load combo boxes with Ajax (code attached)

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>     
  
 
 
省份：
 
  广东 广西 湖南 湖北 安徽  
 
 
 
城市：
 
  --请选择--  
 
 
  

package servlet; import java.io.IOException; import java.io.PrintWriter; import java.util.*; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /** * Servlet implementation class CityByXMLServlet */ @WebServlet("/CityByXMLServlet") public class CityByXMLServlet extends HttpServlet { private static final long serialVersionUID = 1L; private static final String CONTENT_TYPE = "text/xml; charset=UTF-8"; /** * @see HttpServlet#HttpServlet() */ public CityByXMLServlet() { super(); // TODO Auto-generated constructor stub } /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType(CONTENT_TYPE); //设置服务器响应类型 String province =request.getParameter("province"); StringBuffer city = new StringBuffer(""); //记录返回XML串的对象 if("gx".equals(province)){ List list=cityInit(); //获取城市列表 for(int i=0;i"+list.get(i)+""); } }else if("hn".equals(province)){ List list = cityInit1(); //获取城市列表 for(int j=0;j"+list.get(j)+""); } }else if("hb".equals(province)){ List list = cityInit2(); //获取城市列表 for(int j=0;j"+list.get(j)+""); } } city.append(""); PrintWriter out = response.getWriter(); out.println(city.toString()); out.flush(); //输出流刷新 out.close(); //关闭输出流 } /* * 初始化城市 */ public List cityInit2() { List cityList = new ArrayList(); //添加城市列表 cityList.add("武汉"); cityList.add("襄阳"); cityList.add("黄冈"); cityList.add("荆门"); cityList.add("十堰"); cityList.add("黄石"); return cityList; } public List cityInit(){ List cityList = new ArrayList(); //添加城市列表 cityList.add("南宁"); cityList.add("桂林"); cityList.add("北海"); cityList.add("河池"); cityList.add("梧州"); cityList.add("玉林"); return cityList; } public List cityInit1() { List cityList = new ArrayList(); //添加城市列表 cityList.add("长沙"); cityList.add("湘潭"); cityList.add("岳阳"); cityList.add("常德"); cityList.add("衡阳"); cityList.add("邵阳"); return cityList; } /** *当前Servelt的初始化方法. 
 * * @throws ServletException发生ServletExceptio时抛出 */ public void init() throws ServletException { } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

   CityByXMLServlet servlet.CityByXMLServlet   CityByXMLServlet /CityByXMLServlet