JAXB - Unmarshalling List to Map in Java

Question

I need to change List to Map in JAXB unmarshalling file.

The xml file

<jrx:person>
    <jrx:ulement name="id" type="Integer" value="1"/>
    <jrx:ulement name="name" type="String" value="neps"/>
    </jrx:person>

The java classes,

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    @XmlElement(name = "ulement")
    private List<Property> props;
}

@XmlRootElement(name = "ulement")
@XmlAccessorType(XmlAccessType.FIELD)
public class Property {

    @XmlAttribute
    protected String name;

    @XmlAttribute
    private String type;

    @XmlAttribute
    private String value;
}

I have to change the class implementation to

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    @XmlElement(name = "ulement")
    **private Map<String, Property> props;**
}

So that i ll be able to fetch the property using the keys quickly. Please suggest me some implementation to make it work.

---

I have done the following changes but still the values are not mapped,

The classes,

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    @XmlJavaTypeAdapter(value = PropertyAdapter.class)
    private Map<String, Property> map;

}

public class PropertyAdapter extends XmlAdapter<Properties, Map<String, Property>> {

    @Override
    public Properties marshal(Map<String, Property> arg0) throws Exception {
        return null;
    }

    @Override
    public Map<String, Property> unmarshal(Properties p) throws Exception {
        Map<String, Property> map = new HashMap<String, Property>();
        for (Property entry : p.props) { 
            map.put(entry.name, entry);
        }
        return map;
    }

}

public class Properties {

    @XmlElement(name = "ulement")
    public List<Property> props;
}

But the values r Null at ,

@XmlRootElement(name = "person")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    **@XmlJavaTypeAdapter(value = PropertyAdapter.class)
    private Map<String, Property> map;**

}

What exactly is missing over there.

Answer 1

Usually, you would use @XmlJavaTypeAdapter and the XmlAdapter superclass on Person to transform your List into a Map and the opposite.

The problem is that XmlJavaTypeAdapter does not apply to XmlRootElement.

I see two solution to your problem :

1. Executing the adapter logic before marshalling and after unmarshalling.

@XmlRootElement(name = "person",namespace="yourNamespace")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {
    @XmlElement(name ="ulement",namespace="yourNamespace")
    private List<Property> listProperty;

    public Person(AdaptedPerson p){
        this.listProperty = p.getMap().values();
    }

    //getters and setters
}


public class AdaptedPerson {

    private Map<String,Property> map;

    public AdaptedPerson(Person person){
        map = new HashMap<>();
        for(Property p : person.getListProperty()){
            map.put(p.getName(),p);
        } 
    }

    //getters and setters

}

Then each time you unmarshall a person :

AdaptedPerson ap = new AdaptedPerson(p);

And before you marshall an AdaptedPerson :

Person p = new Person(ap);

2. Implementing the map logic directly inside the Person class

@XmlRootElement(name = "person",namespace="yourNamespace")
@XmlAccessorType(XmlAccessType.FIELD)
public class Person {

    @XmlTransient
    private Map<String,Property> map;

    @XmlElement(name ="ulement",namespace="yourNamespace")
    private List<Property> properties;

    public Property getProperty(String name){
        if(map == null) this.init();
        return map.get(name);
    }

    public Property addProperty(Property p){
        if(map == null) this.init();
        map.put(p.getName(),p);
        properties.remove(p);
        properties.add(p);
    }

    public Boolean removeProperty(Property p){
        if(map == null) this.init();
        map.remove(p.getName());
        return properties.remove(p);
    }

    //More methods if you need them.

    private void init(){
        if(properties == null) properties = new ArrayList<>();
        map = new HashMap<>();
        for(Property p : properties){
            map.put(p.getName(),p);
        } 
    }


}

The problem with this method is that for each method of Map you want to use, you will have to code a method that keeps the list updated.