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

user_302343 0
Viewed 121622

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.

jaxb2 jaxb xml java
11 Answers

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/

user_1087850

Jackson has an XmlMapper which will support this out of the box, no need to write any code at all.

Here's a nice tutorial https://www.baeldung.com/jackson-xml-serialization-and-deserialization

Maven dependency:

<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
    <version>2.9.8</version>
</dependency>

For writing a Map to xml:

Map<String, String> map = new HashMap<>();
map.put("SomeKey", "someValue");

XmlMapper mapper = new XmlMapper();
String xml = mapper.writeValueAsString(map);

Will give you

<HashMap><SomeKey>someValue</SomeKey></HashMap>

I was able to customise the root element by creating a HashMap subclass

@JacksonXmlRootElement(localName = "MyRootElement")
public class XmlHashMap<K, V> extends HashMap<K, V>
{

}

So now

Map<String, String> map = new XmlHashMap<>();
map.put("SomeKey", "someValue");

XmlMapper mapper = new XmlMapper();
String xml = mapper.writeValueAsString(map);

Will give you

<MyRootElement><SomeKey>someValue</SomeKey></MyRootElement>
user_17323190

Most people have mentioned about only marshalling here is both marshalling and unmarshalling with Map<String,Object>

import jakarta.xml.bind.JAXBElement;
import jakarta.xml.bind.annotation.XmlAnyElement;
import jakarta.xml.bind.annotation.adapters.XmlAdapter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import javax.xml.namespace.QName;
import lombok.Getter;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;


public class MoxyMapAdapter extends XmlAdapter<MapWrapper, Map<String, Object>> {

  @Override
  public Map<String, Object> unmarshal(MapWrapper value) {
    
    final Map<String, Object> extensions = new HashMap<>();
    //Loop across all elements within value
    for (Object obj : value.getElements()) {
      Element element = (Element) obj;

      final NodeList children = element.getChildNodes();

      if (children.getLength() == 1) {
        extensions.put(element.getNodeName(), element.getTextContent());
      } else {
        List<Object> child = new ArrayList<>();
        for (int i = 0; i < children.getLength(); i++) {
          final Node n = children.item(i);
          if (n.getNodeType() == Node.ELEMENT_NODE) {
            MapWrapper wrapper = new MapWrapper();
            List childElements = new ArrayList();
            childElements.add(n);
            wrapper.elements = childElements;
            child.add(unmarshal(wrapper));
          }
        }
        extensions.put(element.getNodeName(), child);
      }
    }
    return extensions;
  }


  @Override
  public MapWrapper marshal(Map<String, Object> extensions) throws Exception {
    if (extensions == null) {
      return null;
    }

    MapWrapper wrapper = new MapWrapper();

    List elements = new ArrayList();

    //Loop through the Extensions MAP
    for (Map.Entry<String, Object> property : extensions.entrySet()) {

        //If the Value type is MAP then recurse through the loop
        if (property.getValue() instanceof Map) {
          elements
              .add(new JAXBElement<MapWrapper>(new QName(namespaceURI, localPart, prefix), MapWrapper.class, marshal((Map) property.getValue())));
        } else if (property.getValue() instanceof String) {
          // If the Value type is String then directly create JAXBElement
          elements.add(new JAXBElement<String>(new QName(namespaceURI, localPart, prefix), String.class, property.getValue().toString()));
        } else if (property.getValue() instanceof ArrayList) {
          //If the Value type is ArrayList then it contains Duplicate key values so Loop through it
          for (Object dupItems : (ArrayList<String>) property.getValue()) {
            if (dupItems instanceof Map) {
              elements.add(new JAXBElement<MapWrapper>(new QName(namespaceURI, localPart, prefix), MapWrapper.class, marshal((Map) dupItems)));
            } else {
              elements.add(new JAXBElement<String>(new QName(namespaceURI, localPart, prefix), String.class, dupItems.toString()));
            }
          }
        }
    }
    wrapper.elements = elements;
    return wrapper;
  }
}


class MapWrapper {

  @Getter
  @XmlAnyElement
  List elements;
}
user_75842400
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