刚学struts2 checkboxlist帮忙看下

action:import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;import cn.cantalou.bean.User1;import com.opensymphony.xwork2.ActionSupport;public class CheckboxlistAction extends ActionSupport {
private List<String> animals;
private  List<User1> users;
private  Map<Integer,String> fruits;

public List<String> getAnimals() {
return animals;
}
public void setAnimals(List<String> animals) {
this.animals = animals;
}
public List<User1> getUsers() {
return users;
}
public void setUsers(List<User1> users) {
this.users = users;
}
public Map<Integer, String> getFruits() {
return fruits;
}
public void setFruits(Map<Integer, String> fruits) {
this.fruits = fruits;
} public String execute()throws Exception{
animals=new ArrayList<String>(3);
animals.add("Dog");
animals.add("Elephant");
animals.add("Ox");

users=new ArrayList<User1>(3);
users.add(new User1(1,"make"));
users.add(new User1(2,"Tom"));
users.add(new User1(3,"Bill"));

fruits =new HashMap<Integer, String>();
fruits.put(Integer.valueOf(1), "Apple");
fruits.put(Integer.valueOf(2), "Mango");
fruits.put(Integer.valueOf(3), "Orange");

return SUCCESS;

}
}
jsp页面<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Insert title here</title>
</head>
<body>
<h1>checkboxlist Tag Example</h1>
<b>Animals </b><br>
<s:checkboxlist name="animal" list="animals"  ></s:checkboxlist><br><b>User</b><br>
<s:checkboxlist name="User_name"  list="users"  listKey="id" listValue="name"></s:checkboxlist><br><b>Fruits</b><br>
<s:checkboxlist name="fruit_name" list="fruits"  listKey="key" listValue="value"></s:checkboxlist><br></body>
</html>
错误:
org.apache.jasper.JasperException: tag 'checkboxlist', field 'list', name 'fruit_name': The requested list key 'fruits' 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:522)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:389)