将空列表编组为JAXB的缺席节点 [英] Marshal empty lists as absent nodes with JAXB

问题描述

使用JAXB，我想将空白列表编组为不存在的节点.我认为EclipseLink MOXy有这种可能性，但我无法使其正常工作.

Using JAXB I would like to have the possibility to marshal empty lists as absent nodes. I think that EclipseLink MOXy has that possibility, but I can't get it to work.

根据: http://wiki.eclipse.org/User :Rick.barkhouse.oracle.com/Test1 ，您应该可以这样做:

According to: http://wiki.eclipse.org/User:Rick.barkhouse.oracle.com/Test1 you should be able to do it like this:

@XmlElementWrapper(name="line-items", nillable=true)
@XmlNullPolicy(shouldMarshalEmptyCollections=false)
List<LineItem> item = null;

但是

shouldMarshalEmptyCollections

不是有效的属性.

我尝试使用eclipselink 2.4.0、2.4.1和2.5.0-M4.我在做什么错了?

I've tried using eclipselink 2.4.0, 2.4.1 and 2.5.0-M4. What am I doing wrong?

推荐答案

您可以使用 EclipseLink JAXB(MOXy) 的@XmlPath映射来映射此用例.我将在下面的示例中演示如何与使用@XmlElementWrapper进行比较.

You could use EclipseLink JAXB (MOXy)'s @XmlPath mapping to map this use case. I'll demonstrate with an example below how it compares to using @XmlElementWrapper.

根

package forum13268598;

import java.util.List;
import javax.xml.bind.annotation.*;
import org.eclipse.persistence.oxm.annotations.XmlPath;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Root {

    @XmlElementWrapper(name="line-items-element-wrapper")
    List<LineItem> item1 = null;

    @XmlPath("line-items-xml-path/item1")
    List<LineItem> item2 = null;

}

jaxb.properties

要将MOXy用作JAXB提供程序，您需要在与域模型相同的程序包中包含一个名为jaxb.properties的文件，并带有以下条目(请参阅:

To use MOXy as your JAXB provider you need to include a file called jaxb.properties in the same package as your domain model with the following entry (see: http://blog.bdoughan.com/2011/05/specifying-eclipselink-moxy-as-your.html).

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

演示

package forum13268598;

import java.util.ArrayList;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Root.class);

        Root root = new Root();
        root.item1 = new ArrayList<LineItem>();
        root.item2 = new ArrayList<LineItem>();

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(root, System.out);
    }

}

输出

在@XmlElementWrapper用例中，为一个空集合写出一个元素，但在@XmlPath用例中不是.

In the @XmlElementWrapper use case an element is written out for an empty collection, but it is not for the @XmlPath use case.

<?xml version="1.0" encoding="UTF-8"?>
<root>
   <line-items-element-wrapper/>
</root>

这篇关于将空列表编组为JAXB的缺席节点的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！