How do I marshal java.util.List with JAXB like JAX-RS (CXF, and Jersey) do

Question

It seems the latest JAX-RS can handle methods returning java.util.List as the XMLRootElement but normal JAXB cannot. I would like to mimic what CXF and Jersey are doing.

In other words I would like to Marshal a List and just like CXF and Jersey do. Normally if you try to marshal a list with JAXB you get the Root Element exception. How do I get around this with out having to make a wrapping object?

EDIT: Thanks for the many answers but I'm very familiar with the @XmlElementWrapper but that does not even come close to simulating what JAX-RS is doing.

JAX-RS does this:

@XmlRootElement(name="dog")
public class Dog {
    private String name;
    public String getName() { return this.name; }
    //Setter also
}

Now if I serialize a list of dogs:

serialize(List<Dog> dogs);

XML should be (what JAX-RS does):

<dogs>
    <dog><name>Rascal</name></dog>
</dogs>

So you can see I don't want to have to make a wrapper object for every single domain object.

I think this might be the answer https://jaxb.dev.java.net/guide/Different_ways_of_marshalling.html#Marshalling_a_non_element — Adam Gent, May 13 '10 at 15:11
Looks like I could use the code in: org.apache.cxf.jaxrs.provider.AbstractJAXBProvider — Adam Gent, May 13 '10 at 15:46
Unfortunately, the JAX-RS version is also not without its problems, see e.g. this one: http://stackoverflow.com/questions/6192389/root-element-name-in-collections-returned-by-resteasy — Arjan Tijms, May 31 '11 at 22:11
I have seen issues trying to pass a list back through Jersey, so I am not convinced that Rest has solved this issue. — haskovec, Apr 26 '12 at 16:47
I sort of gave up on the issue and just rely on Jackson (JSON) as the serialization technology which thankfully does a damn good job with handling lists. — Adam Gent, Apr 26 '12 at 17:08

score 8 · Answer 1 · edited Dec 13 '11 at 19:11

8

Could you not simply add:

@XmlElementWrapper(name = "wrapperName")

No need to make a wrapper object. This will then be the route element in your marshalled XML response.

edited Dec 13 '11 at 19:11

musefan

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answered Dec 13 '11 at 16:35

Ben

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Yes this is the correct way to ensure collections are wrapped. Annotate your list with the @XmlElementWrapper as per https://docs.oracle.com/javase/7/docs/api/javax/xml/bind/annotation/XmlElementWrapper.html – Steve Swinsburg Nov 25 '14 at 00:34

score 3 · Answer 2 · answered May 02 '12 at 20:10

I have a secret which allows me to avoid screwing with JAXB mappings entirely and have everything work magically.

Have used this approach for years, never spent even 5 minutes worrying about marshalling/unmarshalling. The secret is.... don't use JAXB. :)

In most of my projects which use JAX-RS, I configure Jersey to use xstream and let xstream figure out how to marshal/unmarshal for me. (or jackson for JSON)

Maybe there are some reasons to use JAXB instead of something like xstream/jackson, but I haven't found any yet.

Lately I just rely on Jackson JSON and just forget XML altogether. — Adam Gent, May 03 '12 at 02:18

score 3 · Answer 3 · answered Jan 21 '12 at 05:49

I used a custom iterable list using the following code, hope this helps.

package bindings;

import java.io.Serializable;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlElementWrapper;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlType
@XmlRootElement
public class CustomBindList<V> implements Iterable<V>, Serializable {
        private static final long serialVersionUID = 4449835205581297830L;

        @XmlElementWrapper(name = "List")
        @XmlElement(name = "Entry")
    private final List<V> list = new LinkedList<V>();

    public CustomBindList() {
    }

    public void add(final V obj) {
            list.add(obj);
    }

    public V get(final int index) {
        return list.get(index);
    }

    @Override
    public Iterator<V> iterator() {
        return list.iterator();
    }

    public int size() {
        return list.size();
    }
}

score 1 · Answer 4 · answered Apr 21 '12 at 05:55

1

mapping a List can be done like this..

@XmlAccessorType(XmlAccessType.FIELD)
@XmlType
public class TestRootObject {

  @XmlElement(name = "testList") 
  private List<TestObj> testList;

  //getter setter
}

answered Apr 21 '12 at 05:55

Sanath

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score 1 · Answer 5 · answered May 11 '12 at 11:56

1

check Jackson out, it is very compatible with JAXB bindings and using MappingJsonFactory you can actually interchangeably use Java to XML to Java to Json to Java.

answered May 11 '12 at 11:56

skipy

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score 1 · Answer 6 · answered Jun 01 '12 at 11:45

I annotate my collections with @XmlJavaTypeAdapter(value = Adapter.class). The Adapter class extends from XmlAdapter<key, value> the key is a unique identifier to (un)marshal and the value is your domain object.

Maybe this can help you out. However you do have to create an adapter for every domain object.

score 1 · Accepted Answer · edited May 23 '17 at 12:00

1

Blaise Doughan I believe shows a good solution for this problem here: Is it possible to programmatically configure JAXB?

and

http://blog.bdoughan.com/2012/11/creating-generic-list-wrapper-in-jaxb.html

and somewhat here albeit slightly different use case:

http://blog.bdoughan.com/2012/02/xmlanyelement-and-xmladapter.html

edited May 23 '17 at 12:00

Community

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answered Mar 09 '15 at 17:57

Adam Gent

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How do I marshal java.util.List with JAXB like JAX-RS (CXF, and Jersey) do

7 Answers7

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