how can I add xml attributes to jaxb annotaded class XmlElementWrapper

Question

I have a class with a XmlElementWrapper annotation like:

...

  @XmlElementWrapper(name="myList")
    @XmlElements({
    @XmlElement(name="myElement") }
    )
    private List<SomeType> someList = new LinkedList();

... This code produces XML like

<myList>
  <myElement> </myElement>
  <myElement> </myElement>
  <myElement> </myElement>
</myList>

so far so good.

But now I need to add attributes to the list tag to get XML like

<myList number="2">
  <myElement> </myElement>
  <myElement> </myElement>
  <myElement> </myElement>
</myList>

Is there a 'smart way to achieve this without creating a new class that contains represents the list?

Answer 1

The MOXy JAXB implementation (I'm the tech lead) has an extension (@XmlPath) to handle this case:

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

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

    @XmlPath("myList/@number")
    private int number;

    @XmlElementWrapper(name="myList") 
    @XmlElement(name="myElement") 
    private List<String> someList = new LinkedList<String>();

    public int getNumber() {
        return number;
    }

    public void setNumber(int number) {
        this.number = number;
    }

    public List<String> getSomeList() {
        return someList;
    }

    public void setSomeList(List<String> someList) {
        this.someList = someList;
    } 

}

Will produce the following XML:

<?xml version="1.0" encoding="UTF-8"?>
<root>
   <myList number="123">
      <myElement>FOO</myElement>
      <myElement>BAR</myElement>
   </myList>
</root>

When this code is run:

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.setNumber(123);
        root.getSomeList().add("FOO");
        root.getSomeList().add("BAR");

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

To get this to work using strictly standard JAXB code you will need to use an XML Adapter:

• http://bdoughan.blogspot.com/2010/07/xmladapter-jaxbs-secret-weapon.html

Note:

To use MOXy JAXB you need to add a file called jaxb.properties in with your model classes with the following entry:

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