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

This question already has an answer here: Is it possible to program开发者_运维问答matically configure JAXB? (1 answer) Closed 7 years ago.

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.

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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.

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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();
    }
}

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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.

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mapping a List can be done like this..

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

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

  //getter setter
}

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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.

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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.

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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