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

Question

The question is about JAXB Map marshalling - there is plenty of examples on how to marhsall a Map into a structure like follows:

<map>
  <entry>
    <key> KEY </key>
    <value> VALUE </value>
  </entry>
  <entry>
    <key> KEY2 </key>
    <value> VALUE2 </value>
  </entry>
  <entry>
  ...
</map>

In fact, this is natively supported by JAXB. What I need, however, is the XML where key is the element name, and value is its content:

<map>
  <key> VALUE </key>
  <key2> VALUE2 </key2>
 ...
</map>

I didn't succeed implementing my Map adapter the way it is recommended by JAXB developers (https://jaxb.dev.java.net/guide/Mapping_your_favorite_class.html), as I need, he - dynamic attribute name :)

Is there any solution for that?

P.S. Currently I have to create a dedicated container class for each typical set of key-value pairs I want to marshall to XML - it works, but I have to create way too many of these helper containers.

Answer 1

the code provided didn't work for me. I found another way to Map :

MapElements :

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;
  }
}

MapAdapter :

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;
    }
}

The rootElement :

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;
    }

}

I found the code in this website : http://www.developpez.net/forums/d972324/java/general-java/xml/hashmap-jaxb/