s:doubleselect使用出现问题总结

最近使用s:doubleselect，关联省和地市，出现了跟大家一样的问题，地市显示不出来，ie提示：XXXTemp为空或不是对象。
经反复测试查找，发现问题出现的原因如下：出现其中的一项都可能导致这个问题。
一：doubleName="userId.cityNo"，这样定义是想取的是类中的一个变量，不能这样使用，不能有‘.’出现，必须是cityNo才可以。
二：doubleList="cityList"，cityList必须在public class myclass extends ActionSupport类中定义，不能单独定义出来，也不能在另外的一个类中定义。

我使用的是struts2构建的。

下面是我的代码：
java类：

package tutorial;

import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
import com.opensymphony.xwork2.Validateable;
import com.opensymphony.xwork2.util.OgnlValueStack;

import java.util.LinkedList;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.io.File;

public class UITagExample extends ActionSupport implements Validateable {
List vehicalTypeList = new ArrayList();
    Map vehicalSpecificMap = new HashMap();
public UITagExample() {
       
        VehicalType car = new VehicalType("CarKey", "Car");
        VehicalType motorcycle = new VehicalType("MotorcycleKey", "Motorcycle");
        VehicalType annimal = new VehicalType("annimalKey", "annimal");
        vehicalTypeList.add(car);
        vehicalTypeList.add(motorcycle);
        vehicalTypeList.add(annimal);
       
        List cars = new ArrayList();
        cars.add(new VehicalSpecific("MercedesKey", "Mercedes"));
        cars.add(new VehicalSpecific("HondaKey", "Honda"));
        cars.add(new VehicalSpecific("FordKey", "Ford"));
       
        List motorcycles = new ArrayList();
        motorcycles.add(new VehicalSpecific("SuzukiKey", "Suzuki"));
        motorcycles.add(new VehicalSpecific("YamahaKey", "Yamaha"));
       
        List annimals = new ArrayList();
        annimals.add(new VehicalSpecific("a1Key", "a1"));
        annimals.add(new VehicalSpecific("a2Key", "a2"));
       
        vehicalSpecificMap.put(car, cars);
        vehicalSpecificMap.put(motorcycle, motorcycles);
        vehicalSpecificMap.put(annimal, annimals);
    }  
public List getVehicalTypeList() {
        return vehicalTypeList;
    }
   
    public List getVehicalSpecificList() {
        OgnlValueStack stack = (OgnlValueStack) ServletActionContext.getValueStack(ServletActionContext.getRequest());
        Object vehicalType = stack.findValue("top");
        if (vehicalType != null ){
        if( vehicalType instanceof VehicalType) {
            List l = (List) vehicalSpecificMap.get(vehicalType);
            return l;
        }        }

        return Collections.EMPTY_LIST;
    }
public List getVehicalTypeList() {
        return vehicalTypeList;
    }
   
    public List getVehicalSpecificList() {
        OgnlValueStack stack = (OgnlValueStack) ServletActionContext.getValueStack(ServletActionContext.getRequest());
        Object vehicalType = stack.findValue("top");
        if (vehicalType != null ){
        if( vehicalType instanceof VehicalType) {
            List l = (List) vehicalSpecificMap.get(vehicalType);

            return l;
        }

        }

        return Collections.EMPTY_LIST;
    }
public static class VehicalType {
        String key;
        String description;
        public VehicalType(String key, String description) {
            this.key = key;
            this.description = description;
        }
       
        public String getKey() { return this.key; }
        public String getDescription() { return this.description; }
       
        public boolean equals(Object obj) {
            if (! (obj instanceof VehicalType)) {
                return false;
            }
            else {
                return key.equals(((VehicalType)obj).getKey());
            }
        }
       
        public int hashCode() {
            return key.hashCode();
        }
    }   
   
    public static class VehicalSpecific {
        String key;
        String description;
        public VehicalSpecific(String key, String description) {
            this.key = key;
            this.description = description;
        }
       
        public String getKey() { return this.key; }
        public String getDescription() { return this.description; }
       
        public boolean equals(Object obj) {
            if (! (obj instanceof VehicalSpecific)) {
                return false;
            }
            else {
                return key.equals(((VehicalSpecific)obj).getKey());
            }
        }
       
        public int hashCode() {
            return key.hashCode();
        }
    }
}

jsp代码：
文件uiTagExample.jsp
<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
    <title>UI Tags Example</title>
    <s:head/>
</head>
<body>

<s:actionerror/>
<s:actionmessage/>
<s:fielderror />

<s:form name="test" id="test1"action="example" method="post" enctype="multipart/form-data" tooltipConfig="#{'jsTooltipEnabled':'true'}">
<s:doubleselect
            tooltip="Choose your Vehical"
            label="Favourite Vehical"
            name="favouriteVehicalType"
            list="vehicalTypeList"
            listKey="key"
            listValue="description"
            value="'MotorcycleKey'"
            doubleValue="'YamahaKey'"
            doubleList="vehicalSpecificList"
            doubleListKey="key"
            doubleListValue="description"
            doubleName="favouriteVehicalSpecific" headerKey="-1"
            headerValue="---------- Please Select ----------"
            emptyOption="true" />
</s:form>
   
</body>
</html>

文件index.jsp
<%@ page contentType="text/html; charset=UTF-8" %>
<%@ taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
    <head>
        <title>Hello</title>
        <s:head />  
       
    </head>
    <body>
        <h2 >s:doubleselect</h2 >
<s:form action="uiTagExample">
            Name: <s:textfield name="name" />

            <s:submit />
        </s:form>   

    </body>
</html>


struts.xml文件中加入
<package name="tutorial" extends="struts-default">
        <action name="uiTagExample" class="tutorial.UITagExample">
    <result>uiTagexample.jsp</result>
    <result name="input">uiTagexample.jsp</result>
</action>
    </package>