使用ajax怎么异步读取后台传递回下拉选项的值

<tr>
  <td class="tdcell_word2">请选择展会：</td>
  <td class="tdcell_word3" colspan="3">
<select name="select" id="jieci" onchange="getChange()">
<option value="">选择展会</option>
</select>
<script Language="JavaScript">
loadjieci('- 选择展会 -');
</script>
<span >&nbsp;*</span>
<span  id="mesjieci"></span>
   </td>

</tr>

<script Language="JavaScript">

function loadjieci(str) {
/** 异步加载届次 */
$.getJSON("/DictsAction.do?actionType=jieci",
function (responseData, status) {
if (status != "") {
$("#jieci").empty();
$("<option/>").html("- 选择展会 -").val("- 选择展会 -").appendTo("#jieci");
$(responseData).each(function (n) {

$("<option/>").html(this.name).val(this.code).appendTo("#jieci");

});
//默认显示请选择
$("#jieci").val(str);


} else {
alert("届次加载失败！");
}
});
}

</script>

<!-- ajax异步加载字典 -->
<action path="/DictsAction" type="oa.sys016.oagzxxgl.action.DictsAction" scope="request" />

package oa.sys016.oagzxxgl.action;


import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


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


import net.sf.json.JSONArray;


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 cn.com.chx.bo.AppBo;
/**
 * 通过ajax加载届次选择下拉列表的选择项
 * @author liu
 *
 */
public class DictsAction extends Action{
private AppBo appBo = null;

@Override
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
// 设置编码
response.setContentType("application/json;charset=UTF-8");
response.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();


appBo = new AppBo();


try {


// 获取ActionType
String actionType = request.getParameter("actionType");


if (actionType != null && actionType.equals("jieci")) { // 查询届次
String jieciJson = getJieciJson();
out.print(jieciJson);
}


} catch (Exception e) {
e.printStackTrace();
} finally {
out.close();
}


return null;
}


private String getJieciJson() {
// 查询届次
List jieciList;
try {
jieciList = appBo.query("SELECT ID AS CODE,ZH_NAME AS NAME FROM ZH_GZ_INFOX");


List<Map<String, String>> lists = new ArrayList<Map<String, String>>();


if (jieciList.size() > 0) {
for (int i = 0; i < jieciList.size(); i++) {
Map<String, String> maps = new HashMap<String, String>();
maps.put("code",
(String) ((HashMap) jieciList.get(i)).get("CODE"));
maps.put("name",
(String) ((HashMap) jieciList.get(i)).get("NAME"));

lists.add(maps);


}
}
// [{"id":"1","name":"CIMT2015"},{"id":"2","name":"CCMT2016"}] 
JSONArray json = JSONArray.fromObject(lists);


return json.toString();
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}