Use JAXB XMLAnyElement type of style to return dynamic element names

Question

I have read a lot of answers in these forums, as well as other blog posts, but I can\'t quite seem to connect the pieces together.

So, we start with a basic POJO con

Answer 1

Depends on the solution listed above, I've came into this MapAdapter that addresses both marshaling and unmarshalling process.

@XmlType
public class MapWrapper{
    private List<JAXBElement<String>> properties = new ArrayList<>();

    public MapWrapper(){

    }
    @XmlAnyElement
    public List<JAXBElement<String>> getProperties() {
        return properties;
    }
    public void setProperties(List<JAXBElement<String>> properties) {
        this.properties = properties;
    }
    @Override
    public String toString() {
        return "MapWrapper [properties=" + toMap() + "]";
    }


    public Map<String, String> toMap(){
        //Note: Due to type erasure, you cannot use properties.stream() directly when unmashalling is used.
        List<?> props = properties;
        return props.stream().collect(Collectors.toMap(MapWrapper::extractLocalName, MapWrapper::extractTextContent));
    }

    @SuppressWarnings("unchecked")
    private static String extractLocalName(Object obj){

        Map<Class<?>, Function<? super Object, String>> strFuncs = new HashMap<>();
        strFuncs.put(JAXBElement.class, (jaxb) -> ((JAXBElement<String>)jaxb).getName().getLocalPart());
        strFuncs.put(Element.class, ele -> ((Element) ele).getLocalName());
        return extractPart(obj, strFuncs).orElse("");
    }


    @SuppressWarnings("unchecked")
    private static String extractTextContent(Object obj){
        Map<Class<?>, Function<? super Object, String>> strFuncs = new HashMap<>();
        strFuncs.put(JAXBElement.class, (jaxb) -> ((JAXBElement<String>)jaxb).getValue());
        strFuncs.put(Element.class, ele -> ((Element) ele).getTextContent());
        return extractPart(obj, strFuncs).orElse("");
    }

    private static <ObjType, T> Optional<T> extractPart(ObjType obj, Map<Class<?>, Function<? super ObjType, T>> strFuncs){
        for(Class<?> clazz : strFuncs.keySet()){
            if(clazz.isInstance(obj)){
                return Optional.of(strFuncs.get(clazz).apply(obj));
            }
        }
        return Optional.empty();
    }
}

public class MapAdapter extends XmlAdapter<MapWrapper, Map<String, String>>{

    @Override
    public Map<String, String> unmarshal(MapWrapper v) throws Exception {
        return v.toMap();
    }

    @Override
    public MapWrapper marshal(Map<String, String> m) throws Exception {
        MapWrapper wrapper = new MapWrapper();

        for(Map.Entry<String, String> entry : m.entrySet()){
             wrapper.addEntry(new JAXBElement<String>(new QName(entry.getKey()), String.class, entry.getValue()));
        }

        return wrapper;
    }

}

I've post the full the full post here (in another post), where comments as well as examples are also provided..

Answer 2

I wasn't so far from the answer - after a bit more of experimenting I found the right combo.

Create a wrapper class for the un-mapable return type. Wrapper should contain/return List<JAXBElement<String> Annotate wrapper return type with @XmlAnyElement.

public class MapWrapper {
   @XmlAnyElement
    public List<JAXBElement<String>> properties = new ArrayList<JAXBElement<String>>();
}

Create an XmlAdapter that marshals to the MapWrapper

public class MapAdapter extends XmlAdapter<MapWrapper, Map<String,String>> {
    @Override
    public MapWrapper marshal(Map<String,String> m) throws Exception {
    MapWrapper wrapper = new MapWrapper();
    List<JAXBElement<String>> elements = new ArrayList<JAXBElement<String>>();
       for (Map.Entry<String, String> property: m.entrySet()) {
          elements.add(new JAXBElement<String>(
                    new QName(getCleanLabel(property.getKey())), 
          String.class, property.getValue()));
       }
       wrapper.elements=elements;
    return wrapper;
}

@Override
public Map<String,String> unmarshal(MapWrapper v) throws Exception {
            // TODO
    throw new OperationNotSupportedException();
}

// Return a lower-camel XML-safe attribute
private String getCleanLabel(String attributeLabel) {
    attributeLabel = attributeLabel.replaceAll("[()]", "")
            .replaceAll("[^\\w\\s]", "_").replaceAll(" ", "_")
            .toUpperCase();
    attributeLabel = CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL,
            attributeLabel);
    return attributeLabel;
}
}

Annotate your unmappable type with the XmlAdapter

@XmlRootElement
public class SomeBean {

    @XmlJavaTypeAdapter(MapAdapter.class)
    public LinkedHashMap<String, String> getProperties() {
        return properties;
    }
}

A map like:

My Property 1    My Value 1 
My Property 2    My Value 2

Should come out as:

<someBean>
   <properties>
     <myProperty1>My Value 1</myProperty1>
     <myProperty2>My Value 1</myProperty2>
   </properties>
</someBean>

Hope this helps someone else!