JAXB: how to marshall map into <key>value</key>

package com.cellfish.mediadb.rest.lucene;

import javax.xml.bind.annotation.XmlElement;

class MapElements
{
@XmlElement public String  key;
@XmlElement public Integer value;

private MapElements() {} //Required by JAXB

public MapElements(String key, Integer value)
{
this.key   = key;
this.value = value;
}
}

import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.annotation.adapters.XmlAdapter;

class MapAdapter extends XmlAdapter<MapElements[], Map<String, Integer>> {
public MapElements[] marshal(Map<String, Integer> arg0) throws Exception {
MapElements[] mapElements = new MapElements[arg0.size()];
int i = 0;
for (Map.Entry<String, Integer> entry : arg0.entrySet())
mapElements[i++] = new MapElements(entry.getKey(), entry.getValue());

return mapElements;
}

public Map<String, Integer> unmarshal(MapElements[] arg0) throws Exception {
Map<String, Integer> r = new HashMap<String, Integer>();
for (MapElements mapelement : arg0)
r.put(mapelement.key, mapelement.value);
return r;
}
}

import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement
public class Root {

private Map<String, Integer> mapProperty;

public Root() {
mapProperty = new HashMap<String, Integer>();
}

@XmlJavaTypeAdapter(MapAdapter.class)
public Map<String, Integer> getMapProperty() {
return mapProperty;
}

public void setMapProperty(Map<String, Integer> map) {
this.mapProperty = map;
}

}