how to unmarshall only the single nested element using javax.xml.bind.Unmarshaller

Question

I have a following sample xsd

 <annotation><appinfo>
<jaxb:schemaBindings>
    <jaxb:package name="com.myapp"/>
</jaxb:schemaBindings>
</appinfo></annotation>
<element name="user">
    <complexType>
        <sequence>
            <element name="roles" type="u:Roles" minOccurs="1"></element>
        </sequence>
        <attribute name="name" type="string"></attribute>
    </complexType>
</element>

<complexType name="Role">
    <complexContent>
        <extension base="u:Role">
            <attribute name="name" type="string"></attribute>
            <attribute name="action" type="string"></attribute>
        </extension>
    </complexContent>
</complexType>

I want to unmarshall only a Roles xml like the sample as follows

        JAXBContext c = JAXBContext.newInstance(User.class, Roles.class, Role.class);
    Unmarshaller unmarshaller = c.createUnmarshaller();
    JAXBElement ele = (JAXBElement) unmarshaller.unmarshal(inputStream);
    return (Roles) ele.getValue();

My input stream/xml is

<roles>
    <role name="admin" action="all"/>
    <role name="recep" action="select"/>
</roles>

The above code throws the following error

javax.xml.bind.UnmarshalException: unexpected element (uri:"http://www.myapp.com/xsd/internal/myapp", local:"roles"). Expected elements are <{http://www.myapp.com/xsd/internal/myapp}User>

How to get my roles xml to be unmarshall?

Answer 1

If you know the class you want to unmarshal, use the unmarshal(Source source, Class<T> declaredType) and likes.

So try unmarshaller.unmarshall(source, Roles.class) which would give you JAXBElement<Roles>. You can then getValue() from it to get an instance of Roles.

If you provide the class for unmarshalling, the root element name does not matter at all, JAXB does not neet to "know" it.