java - 如何在 Spring 中将 AutopopulatedList 引用到 List ？

Question

我正在尝试使用 AutoPopulateList 创建动态填充列表。我还有一个表单对象，如下面的代码所示:

public class CDNoteForm{

    private AbstractCDNote cdnote;
    private List<? extends AbstractInvoiceItem> invoiceItemList ;


    public CDNoteForm() {
        super();
    }
    public CDNoteForm(String type){
        super();
        if(type.equals("cdnote")){
            this.invoiceItemList =  new AutoPopulatingList<CDNoteItem>(CDNoteItem.class);
        }
        else if(type.equals("vendorcdnote")) {          
            this.invoiceItemList =  new AutoPopulatingList<VendorCDNoteItem>(VendorCDNoteItem.class);
        }

    }

    public AbstractCDNote getCdnote() {
        return cdnote;
    }
    public void setCdnote(AbstractCDNote cdnote) {
        this.cdnote = cdnote;
    }
    public List<? extends AbstractInvoiceItem> getInvoiceItemList() {
        return invoiceItemList;
    }
    public void setInvoiceItemList(List<? extends AbstractInvoiceItem> invoiceItemList) {
        this.invoiceItemList = invoiceItemList;
    }
}

表单对象正在我的 Controller 中的方法中声明，如下所示。

@RequestMapping(value ="/cdnote/create"  , method = RequestMethod.GET)
    public String getCreateCDNotePage(Model model){

    CDNoteForm cdnoteForm = new CDNoteForm("cdnote");
    model.addAttribute("CDNoteForm" , cdnoteForm);
    return "AddCDNote";
}

“invoiceItemList”在 jsp 中被引用，如下所示

<form:input type="text" id="Quantity0"  path="invoiceItemList[0].quantity" class="form-control"></form:input>                       

两个类“CDNoteItem”和“VendorCDNoteItem”扩展了抽象类“AbstractInvoiceItem”。现在我在编译时没有收到任何错误，但是当我尝试运行它并访问该页面时，我在控制台上收到以下错误。

SEVERE: Servlet.service() for servlet [SpringGST] in context with path [/SpringGST] threw exception [org.springframework.beans.InvalidPropertyException: Invalid property 'invoiceItemList[0]' of bean class [com.gst.FormObjects.CDNoteForm]: Illegal attempt to get property 'invoiceItemList' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'invoiceItemList' of bean class [com.gst.FormObjects.CDNoteForm]: Could not instantiate property type [com.gst.models.AbstractInvoiceItem] to auto-grow nested property path: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.gst.models.AbstractInvoiceItem]: Is it an abstract class?; nested exception is java.lang.InstantiationException] with root cause
org.springframework.beans.NullValueInNestedPathException: Invalid property 'invoiceItemList' of bean class [com.gst.FormObjects.CDNoteForm]: Could not instantiate property type [com.gst.models.AbstractInvoiceItem] to auto-grow nested property path: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.gst.models.AbstractInvoiceItem]: Is it an abstract class?; nested exception is java.lang.InstantiationException

我不明白为什么当“invoiceItemlist”引用其子类的自动填充列表进行初始化时，它试图实例化抽象类“AbstractInvoiceItem”

Answer 1

你可以使用invoiceItemList.get(0)代替invoiceItemList[0]并尝试