After a discussion, it seems that using the example provided by the Jackson doc didn't work out of the box.

I still wonder, if that wouldn't be because the example was used as is. This should work in theory:

    public Set<Object> getSingletons() {
        HashSet<Object> singletons = new HashSet<Object>(super.getSingletons()); //Note that we call the getSingletons from the super class here, to avoid breaking anything.
        singletons.add(new org.codehaus.jackson.jaxrs.JacksonJaxbJsonProvider());
        return singletons;
    }