struts+Ajax的2级联动菜单

首先需要把以下JS粘到 jsp页面的javascript标签中：
<script type="text/javascript">
var xmlHttp;
var xmlDOM=new ActiveXObject("Microsoft.XMLDOM");
xmlDOM.async=false;//是否异步更新

//创建XMLHttpRequest对象
function createXMLHttpRequest(){
  if(window.ActiveXObject){
  //如果用户使用IE，就返回XMLHTTP的ActiveX对象
    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
  }
  else if(window.XMLHttpRequest){
  //否则返回一个XMLHttpRequest对象
    xmlHttp = new XMLHttpRequest();
  }
}
function getregion(){
createXMLHttpRequest();
try{//document.form1.d_device_id
   //post方式传递参数
   xmlHttp.onreadystatechange = handleStateGetRetion;
   var d_device_id=document.getElementById("d_device_id").value;
   var post="d_device_id="+d_device_id; 
   //alert(d_device_id);
   xmlHttp.open ('post',"<%=path%>/getregion.do",true);
   xmlHttp.setrequestheader("cache-control","no-cache");
   xmlHttp.setrequestheader("Content-Type","application/x-www-form-urlencoded");
   xmlHttp.send (post);//注意:POST方式，使用这个来发送内容?
   }catch(exception){
   alert("您要访问的资源不存在!");
   }
}
function handleStateGetRetion(){
    if(xmlHttp.readyState == 4){
      if (xmlHttp.status == 200 || xmlHttp.status == 0){
        // 取得XML的DOM对象
       
          var res=xmlHttp.responseXML.getElementsByTagName("res")
          //alert(res);
          var list = document.all.d_ifindex;
          list.options.length=0;
          list.add(new Option("---请选择---",""));
          for(var i=0;i<res.length;i++){
              list.add(new Option(res[i].firstChild.data,res[i].firstChild.data));
          }

       }
   }
}
</script>

下面是HTML代码（本人只选取其中2个下拉菜单拿过来做演示例子）：
<tr bgcolor="#E3F3FD">
    <td align="right">主动标识:</td>
    <td><label>
     <select id="d_device_id" name="d_device_id" class="select" onChange="getregion();">
                      <option value="">--请选择--</option>
    <%=(String)request.getAttribute("str") %>
             这里是第一个菜单中(主动菜单)的选项，在这里我就不给大家把这里列出来了.可以查询出一个带“<option>”标签的String字符串，到这得到便可
      </select>  
    </label>
    <label></label></td>
  </tr>

  <tr bgcolor="#E3F3FD">
    <td align="right">目标联动标识: </td>
    <td> <label>                  
<select id="d_ifindex" name="d_ifindex"   class="select">
                
                  </select>
                 </label>
                   </td>
  </tr>  



再下边就是后台的struts类：
package com.snmp.action;

import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.*;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;

import com.snmp.util.DB;

/**
*
* 联动下拉菜单
* @author 徐彬
* 2009-06-25
*
*/

public class GetRegionAction extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {

Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
response.setContentType("text/xml; charset=UTF-8");

response.setCharacterEncoding("UTF-8");
response.setHeader("Cache-Control", "no-cache");
List cities = new ArrayList();
PrintWriter out = response.getWriter();
String d_device_id = request.getParameter("d_device_id");

try {
conn = DB.getConnection();
stmt = conn.createStatement();
String sql = "select device_id, ifindex, port_desc, speed from snmp_port where device_id='"+d_device_id+"'";
//String strtwo=DB.getSelectOption(sql, "");
    rs=stmt.executeQuery(sql);
    while (rs.next())
    {
        cities.add(rs.getString(2));
    }
   
    DB.releaseCursor(conn, stmt, rs);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
      
        out.println("<response>");
        for(int i=0;i<cities.size();i++)
        {
            out.println("<res>" + cities.get(i).toString() + "</res>");
                   }
        out.println("</response>");
        out.close();

return null;

}
}