Question

我有这堂课：

PreApprovalRequest类有一个属性headings，它会在控制器中自动填充（参见页面上控制器的代码）。

public class PreApprovalRequest {
    private Long id;
    private String Description;
    private Collection<Headings> headings; //this property!
}

控制器：

@Controller
@SessionAttributes({"preApprovalRequest", "productRecommendations"})
public class RequestController {

    @RequestMapping(value = "/submit",  method = RequestMethod.POST)
    public String submitResults(@ModelAttribute(value = "preApprovalRequest") @Valid PreApprovalRequest preApprovalRequest, BindingResult errors) {
        //HERE: It looks like if I have some headings in the preApprovalRequest object already, the call of this method will not delete those, but will append to the existing list.
        //save object in DB.
        return "dashboard";
    }
}

知道如何让Spring替换集合对象而不是添加它吗？

Answer 1

我如何理解您的问题，您无法将headings个集合替换为Headings的新集合。你不能用以下方式做到吗？

preApprovalRequest.setHeadings(new ArrayList<Headings>());
preApprovalRequest.getHeadings().add(heading1);

Answer 2

即使是您第一次提交表单，是否会发生这种情况？如果没有，请在完成控制器中的所有操作后尝试清理缓存。

在方法中添加SessionStatus并调用“setComplete（）”来清除属性。因此，第二次启动进程时，缓存将为空，您将不得不使用新的preApprovalRequest

@RequestMapping(value = "/submit",  method = RequestMethod.POST)
public String submitResults(@ModelAttribute(value = "preApprovalRequest") @Valid PreApprovalRequest preApprovalRequest, BindingResult errors, SessionStatus status) {
    /HERE: It looks like if I have some headings in the preApprovalRequest object already, the call of this method will not delete those, but will append to the existing list.
    //save object in DB.

    status.setComplete();
    return "dashboard";
}

Answer 3

如果您正在寻找的是动态缩小/扩展类型的List，那么集合必须是lazy.Apache commons集合提供了一个Lazy List类来执行此操作。您可以从{{3}获取apache commons集合}

因此您的控制器模型可以重写为：

public class PreApprovalRequest {
    private Long id;
    private String Description;
    private List headings;

    public PreApprovalRequest()
    {
        headings=LazyList.decorate(
           new ArrayList(),
           FactoryUtils.instantiateFactory(Header.class));
    }

}

将数据绑定到列表背后的想法是，在html元素名称属性中跟踪列表项索引：

<c:forEach item="${modelAttr.list}" varStatus="listItem">

<form:input type="text" path="list[${listItem.index}]" />

</c:forEach>

@ModelAttribute有Collection属性 - 值被添加到集合中，而不是被替换？

3 个答案: