How can I add xml attributes to jaxb annotated 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

I got a better solution for your question.

For making Xml Java object, use the following code:

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

@XmlRootElement(name="myList")
public class Root {

    private String number;
    private List<String> someList;

    @XmlAttribute(name="number")
    public String getNumber() {
        return number;
    }

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

    @XmlElement(name="myElement")
    public List<String> getSomeList() {
        return someList;
    }

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

    public Root(String numValue,List<String> someListValue) {
        this();
        this.number = numValue;
        this.someList = someListValue;  
    }

    /**
     * 
     */
    public Root() {
        // TODO Auto-generated constructor stub
    }

}

To run the above code using JAXB, use the following:

   import java.util.ArrayList;
import java.util.List;

import javax.xml.bind.*;

public class Demo {

        public static void main(String[] args) throws Exception {
            List<String> arg = new ArrayList<String>();
            arg.add("FOO");
            arg.add("BAR");
            Root root = new Root("123", arg);

            JAXBContext jc = JAXBContext.newInstance(Root.class);
            Marshaller marshaller = jc.createMarshaller();
            marshaller.marshal(root, System.out);
        }
}

This will produce the following XML as the output:

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

I think this is more helpful you.

Thanks..

Answer 2

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

Answer 3

If you are not using MOXy or just want to stick to standard JAXB annotations, you can extend upon Noby's answer to add support for a generic wrapper class. Noby's answer only currently supports a list of strings, but say for example you're going to be using the same generic wrapper class for several different classes. In my example, I want to create a generic "PagedList" class that will marshall to something that looks like a list, but also contains information about the page offset and the total number of elements in unpaged list.

The one downside of this solution is that you have to add additional @XmlElement mappings for each type of class that will be wrapped. Overall though, probably a better solution than creating a new class for each pagable elements.

@XmlType
public class PagedList<T> {
    @XmlAttribute
    public int offset;

    @XmlAttribute
    public long total;

    @XmlElements({
        @XmlElement(name="order", type=Order.class),
        @XmlElement(name="address", type=Address.class)
        // additional as needed
    })
    public List<T> items;
}

@XmlRootElement(name="customer-profile")
public class CustomerProfile {
    @XmlElement
    public PagedList<Order> orders;
    @XmlElement
    public PagedList<Address> addresses;
}

Marshalling this example would get you:

<customer-profile>
    <order offset="1" total="100">
        <order> ... </order>
        <order> ... </order>
        <order> ... </order>
        ...
    </orders>
    <addresses offset="1" total="5">
        <address> ... </address>
        <address> ... </address>
        <address> ... </address>
        <address> ... </address>
        <address> ... </address>
    <addresses>
</customer-profile>

Hope that helps. This is the solution that I settled upon at least.