REST how to return list of Interface

Question

I have a class FoodItemImpl which implements the interface FoodItem .

I want to return list of FoodItem using REST.

I couldn't

However, I can return list of FoodItemImpl like this:

Wraper

enum wria {
    instance;
    private Map<Integer, FoodItemImpl> map = new HashMap<Integer, FoodItemImpl>();

    public Map<Integer, FoodItemImpl> get() {
        return this.map;
    }

    wria() {
        List<FoodItem> LL = FoodItemImpl.getAllFoodItems();
        for (int i = 0; i < LL.size(); i++) {
            map.put(LL.get(i).getID(), (FoodItemImpl) LL.get(i));
        }
    }
}

REST Code

@GET
    @Produces({ MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON })
    public List<FoodItemImpl> getXML() {
        List<FoodItemImpl> ll = new LinkedList<FoodItemImpl>();
        ll.addAll(wria.instance.get().values());
        return ll;
    }

Answer 1

Your error states that you do not have a message body writer for the interface FoodItem to the type application/xml. Now, assuming you are using JAXB as default mbw for XML:

JAXB cannot bind interfaces out of the box . You have to create an adapter:

public class AnyFoodItemAdapter extends XmlAdapter<Object,Object> {
    Object unmarshal(Object v) { return v; }
    Object marshal(Object v) { return v; }
}

And then annotate FoodItem:

@XmlJavaTypeAdapter(AnyFoodItemAdapter .class)
interface FoodItem {
    ...
}

See more details and other ways of doing this in: Project JAXB - Mapping Interfaces .

Answer 2

Try annotating your Interface Getter Methods (JAXB) to define the elements in your result XML. That should resolve your issue, I believe.

Instead of returning List, try having another XmlElement class (Interface if you want) which holds a list for you.