接口类型数据绑定的Spring List - 如何？

Question

试图在网上找到答案，但失败了。对于专业的 Spring 开发人员来说应该很简单......所以它来了：

简而言之，我想将接口类型列表绑定：列表到表单并取回数据（可能由用户通过表单修改。问题是它不起作用:(

我的代码（短版） - 传递给表单的命令/模型类：

public class RoomsFormSearchResultCommand extends RoomsFormSearchCommand {
    @SuppressWarnings("unchecked")
    private List<IRoom> roomsList = LazyList.decorate(new ArrayList<Room>(),
            FactoryUtils.instantiateFactory(Room.class));

    public List<IRoom> getRoomsList() {
        return roomsList;
    }

    public void setRoomsList(final List<IRoom> roomsList) {
        this.roomsList = roomsList;
    }

(...)

然后以我使用它的形式（短版）：

    <form:form method="post" action="reserve" commandName="roomsResultsCmd">
(...)
    <c:forEach var="room" items="${roomsResultsCmd.roomsList}"
                varStatus="status">
                <tr>
                    <td><form:input path="roomsList[${status.index}].roomNumber" readonly="true"/>
(...)

表单显示正常，但提交后我得到：

2012-01-22 21:31:55 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [wyspa] in context with path [/wyspa] threw exception [Request processing failed; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'roomsList[0]' of bean class [com.wyspa.controller.command.RoomsFormSearchResultCommand]: Illegal attempt to get property 'roomsList' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'roomsList' of bean class [com.wyspa.controller.command.RoomsFormSearchResultCommand]: Could not instantiate property type [com.wyspa.entity.IRoom] to auto-grow nested property path: java.lang.InstantiationException: com.wyspa.entity.IRoom] with root cause
org.springframework.beans.NullValueInNestedPathException: Invalid property 'roomsList' of bean class [com.wyspa.controller.command.RoomsFormSearchResultCommand]: Could not instantiate property type [com.wyspa.entity.IRoom] to auto-grow nested property path: java.lang.InstantiationException: com.wyspa.entity.IRoom
    at org.springframework.beans.BeanWrapperImpl.newValue(BeanWrapperImpl.java:633)
    at org.springframework.beans.BeanWrapperImpl.growCollectionIfNecessary(BeanWrapperImpl.java:863)
    at org.springframework.beans.BeanWrapperImpl.getPropertyValue(BeanWrapperImpl.java:770)
    at org.springframework.beans.BeanWrapperImpl.getNestedBeanWrapper(BeanWrapperImpl.java:555)

(...)

然后，当我将列表更改为“实例”列表时，一切正常！

public class RoomsFormSearchResultCommand extends RoomsFormSearchCommand {
    @SuppressWarnings("unchecked")
//notice that the List is now List<Room>
    private List<Room> roomsList = LazyList.decorate(new ArrayList<Room>(),
            FactoryUtils.instantiateFactory(Room.class));

在这种情况下，数据以正确的方式传递给控制器​​。

由于我习惯于在接口上进行开发并且对此非常着迷，我真的不希望将List<IRoom>（从服务返回）翻译成似乎适合 Spring 的List<Room>。在这种情况下是否可以使用 List<IRoom> 或者 Spring 不支持它？

//Room当然实现了IRoom——但我猜你已经明白了……

如果有任何帮助/建议，我将非常高兴！

最好的问候， 尼尔万

Answer 1

试试下面几行

@SuppressWarnings("unchecked")
private List<IRoom> roomsList = LazyList.decorate(new ArrayList<IRoom>(),
    FactoryUtils.instantiateFactory(Room.class));

我自己没有时间尝试，但它会很有意义。

Answer 2

我有完全相同的问题。更改为关注不会解决问题。看起来 spring 绑定忽略了工厂工具并尝试实例化 null 对象本身：

@SuppressWarnings("unchecked")
private List<IRoom> roomsList = LazyList.decorate(new ArrayList<IRoom>(),
    FactoryUtils.instantiateFactory(Room.class));

解决方法是在控制器中关闭自动增长嵌套路径：

@InitBinder protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) {
    binder.setAutoGrowNestedPaths(false);
    super.initBinder(request, binder);
 }

问题是您会丢失方便的嵌套路径，例如 user.account.address.street。您必须确保用户、帐户、地址都不为空。它确实会引起很多问题。这就是我来这里的原因，看看我是否能找到更好的解决方案。

Answer 3

如果您实际上不需要列表自动增长，则可以将表单对象存储在会话中，以避免禁用自动增长嵌套路径的不良副作用。

@Controller
@SessionAttributes(types = RoomsFormSearchResultCommand.class)
public final class SearchController {

    @InitBinder
    protected void initBinder(final WebDataBinder binder) {
            binder.setAutoGrowNestedPaths(false);
    }

    @RequestMapping(method = RequestMethod.GET)
    public String showForm(final Model model) {
            RoomsFormSearchResultCommand form = ... // create or load form
            model.addAttribute(form); 
    }

    @RequestMapping(method = RequestMethod.POST)
    public String onSubmitUpdateCart(
                    @ModelAttribute final RoomsFormSearchResultCommand form,
                    final BindingResult result,
                    final SessionStatus status) {
            // if result has no errors, just set status to complete
            status.setComplete();
    }
}