Marshal empty lists as absent nodes with JAXB

问题

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.

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;

But

shouldMarshalEmptyCollections

is not a valid property.

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

回答1:

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.

Root

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

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

Demo

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);
    }

}

Output

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>

来源：https://stackoverflow.com/questions/13268598/marshal-empty-lists-as-absent-nodes-with-jaxb

标签

java

xml

jaxb

moxy