select cascade realization

----------表单
<td>
<select name="appld", id="nappld" style="vertical-align: middle;" onchangeg="changeApp()">
<option value="">请送择</options>
<c:forEach items="${appInfoList}" var="app">
<option value="${app.appld }"
<c: if test="${user.appld ==app.appld}">selected</c: if>>${app.appName}
</option>
</c:forEach>
</select>
</td>

--------js
function changeApp() {
if($(#appld).val() != ''){
var url = 'user/listRole.html?appId='+$(#appld).val();
$.post(url, function (data) {
var options = "<option value=''>请选择</option>";
if(data.length>0){
for(var i=0;i<data.length;i++) {
options += "<option value="+data[i].roleId+">"+data[i].roleName+"</option>";
}
$("#roleId").html(options);
})；
} else {
var options = ”<option value=''>请选择</option>”；
$("#roleId").html(options);
}
}
}

-----后台获取数据
@RequestMapping(value = "listRole", method = RequestMethod.post)br/>@ResponseBody
public Lisc<Role> listRole(String appld, Model model,
HttpServletRequest request) throws CrsException {
List<Role> roleList = roleService.getRoleListByAppId(appId);
return roleList;
}
-----数据实体
package com.aacec.model;
isporc java.io.Serializable;
public class Role implements Serializable {
private Integer roleld;
private String roleName;
private String rights?
private String parentld;
private String appld;
private String appName;
private String userid;// Teddy
.......