为什么用struts2.0的iterator标签，JSP页面中无法显示？

查询方法：  public   void toDelete(String[] teskId) {
        
    String sqlString = "delete from TTesk where TeskId = '" +teskId+"'" ;
    
System.out.println("---------------------"+sqlString+"-----------------------------");
    
//Query query = session.createQuery(sqlString);

session.update(sqlString);

transaction.commit();

HibernateSessionFactory.closeSession();
}action中的方法：
 List list = TeskFactory.getInstance().toSelect();

request.setAttribute("UnTesk", list);


return null;
}
JSP页面：                       <form name="form1" action="UnTeskList.action" method="POST">
        <table cellspacing="1" class="table">
 <tr class="table_header">
   <td
任务名称
   </td>
   <td>
 实施人
   </td>
   <td>
          开始时间
   </td>
   <td>
          结束时间
   </td>
   <td>
 任务状态
   </td>
   <td>
   
                               </td>
</tr>
                               
                               <s:iterator id="UnTeskList" value="#request.UnTesk">
   <tr class="row2" onMouseOver="this.className='row1'"
onMouseOut="this.className='row2'">
<td>
  <s:property id="UnTeskList" value="#UnTeskList.teskName"/>
 </td>
 <td>
  <s:property id="UnTeskList" value="#UnTeskList.empId"/>
 </td>
 <td>
 <s:property id="UnTeskList" value="#UnTeskList.teskDate"/>
  </td>
  <td>
 <s:property id="UnTeskList" value="#UnTeskList.teskEnd"/>
  </td>
  <td>
  <s:property id="UnTeskList" value="#UnTeskList.teskState"/>
  </td>
  <td>
  <input type="checkbox" name="taskId" value="">
           </td>
      </tr>
                                </s:iterator>

</table>
   <p align=right style="padding-right: 30px" >
<input type="button" Class="button" value="删除&raquo;"                           size="8"onClick="deleteTask  ();" />
</p>                           </form>