struts2 select标签 获取 Action值 报错

定义的 测试类
public class cs {
    public  int no;
    public String va;
    
    public void setNo(int no){
        this.no = no;
    }
    public int getNo(){
        return no;
    }
    
    public void setVa(String va){
        this.va = va;
    }
    public String getVa(){
        return va;
    }
    
    public void cs(int no,String va){
        this.no = no;
        this.va = va;
    }
    public void cs(){}
}
struts2配置
<action name="cs" class="test.cszyAction">
             <result name="success" type="redirect">input.jsp</result>
        </action>定义的cszyAction 填充alist 测试用的
public class cszyAction extends ActionSupport{
    private  List<cs> alist=new ArrayList<cs>();    public void setAlist (List<cs> list){
        this.alist = list;
    }
    public List<cs> getAlist(){
        return alist;
    }
    public String execute() throws Exception {
        List mylist = new ArrayList<cs>();
       cs cs1 = new cs();
        cs1.no=1;cs1.va="A";
        mylist.add(cs1);
        cs cs2 = new cs();
        cs2.no=2;cs2.va="B";
        mylist.add(cs2);
        cs cs3 = new cs();
        cs3.no=3;cs3.va="C";
        mylist.add(cs3);
        cs cs4 = new cs();
        cs4.no=4;cs4.va="D";
        mylist.add(cs4);
        cs cs5 = new cs();
        cs5.no=5;cs5.va="E";
        mylist.add(cs5);
        cs cs6 = new cs();
        cs6.no=6;cs6.va="F";
        mylist.add(cs6);
        this.setAlist(mylist);
        return SUCCESS;
    }
}
首页 用来初始化Action 点击按钮时初始化cszyAction 并跳转到需要测试的页面 index.jsp
<s:form name="form1" action="cs">
    <s:submit label="submit"></s:submit>
</s:form>
最终的测试页面input.jsp 用来显示<s:select>标签
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title></title>
  </head>
  <body>
    <s:form name="form1" action="cs" method="POST">
        <a href="login.jsp" >hellow </a>
        <s:select list="alist" listKey="no" listValue="va" />
    </s:form>
  </body>
</html>
结果报错
type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: tag 'select', field 'list': The requested list key 'alist' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:527)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88)
root cause tag 'select', field 'list': The requested list key 'alist' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]
org.apache.struts2.components.Component.fieldError(Component.java:237)
org.apache.struts2.components.Component.findValue(Component.java:358)
org.apache.struts2.components.ListUIBean.evaluateExtraParams(ListUIBean.java:80)
org.apache.struts2.components.Select.evaluateExtraParams(Select.java:105)
org.apache.struts2.components.UIBean.evaluateParams(UIBean.java:858)
org.apache.struts2.components.UIBean.end(UIBean.java:510)
org.apache.struts2.views.jsp.ComponentTagSupport.doEndTag(ComponentTagSupport.java:42)
org.apache.jsp.input_jsp._jspx_meth_s_005fselect_005f0(input_jsp.java:148)
org.apache.jsp.input_jsp._jspx_meth_s_005fform_005f0(input_jsp.java:111)
org.apache.jsp.input_jsp._jspService(input_jsp.java:69)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:88)有高人能解答吗