Ajax实现动态加载组合框的实例代码

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);
 }
}

CityByXMLServletservlet.CityByXMLServletCityByXMLServlet/CityByXMLServlet