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Editorial Team
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Asked: 2026-05-26T09:50:09+00:00

I have to generate a xml element that can have as value any primitive

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I have to generate a xml element that can have as value any “primitive type” (xsd:string, xsd:boolean, etc). Examples:

<field xsi:type="xsd:string" name="aString">String Value</field>
<field xsi:type="xsd:date" name="aDate">2011-10-21</field>
...

So, I tried two implementations:

public class Field {
    @XmlAttribute
    private String name;

    @XmlValue
    Object value;
}

and …

public class Field<T> {
    @XmlAttribute
    private String name;

    @XmlValue
    T value;
}

I’m testing this with:

Marshaller marshaller = JAXBContext.newInstance(Field.class).createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
marshaller.setProperty("com.sun.xml.bind.xmlDeclaration", Boolean.FALSE);

Field field = new Field();
field.name = "name";
field.value = "value";

ByteArrayOutputStream stream = new ByteArrayOutputStream();
marshaller.marshal(field, new PrintWriter(stream));
System.out.println(stream);

But I’m getting this NullPointerException when I try to instantiate the JAXBContext. 

java.lang.NullPointerException
at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor.get(TransducedAccessor.java:165)
at com.sun.xml.bind.v2.runtime.property.ValueProperty.<init>(ValueProperty.java:77)
at com.sun.xml.bind.v2.runtime.property.PropertyFactory.create(PropertyFactory.java:106)
at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.<init>(ClassBeanInfoImpl.java:179)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:515)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:330)
at

The idea is allow schema validation for the field element (It is define in a schema must its type will be set in each instance). So, even is this a Bug (or not) … how JAXB will put the correct xsi:type to this field instance? I’m missing a concept here?

I know that maybe the problem is the usage of the @XmlValue because of this restrictions (from the javadoc):

  • At most one field or property can be annotated with the @XmlValue annotation.
  • @XmlValue can be used with the following annotations: XmlList. However this is redundant since XmlList maps a type to a simple schema type that derives by list just as XmlValue would.
  • If the type of the field or property is a collection type, then the collection item type must map to a simple schema type.
  • If the type of the field or property is not a collection type, then the type must map to a XML Schema simple type.

… because an Object or a generic T is not necessarily a XML Schema simple type, this approach seems not to be the correct one …

Thanks in advance …

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1 Answer

  1. Editorial Team

    I have confirmed the issue you are seeing in both the reference and EclipseLink JAXB (MOXy) implementations of JAXB. The problem you are seeing is due to use of @XmlValue. If the value property was mapped as an @XmlElement you would see the xsi:type attribute appear as expected.

    I have entered the following bug to track this issue in EclipseLink JAXB (MOXy):

    Depending upon what your domain model looks like you may be interested in the @XmlPath extension from EclipseLink JAXB (MOXy):

    UPDATE

    This issue has now been fixed in the EclipseLink 2.3.3 and EclipseLink 2.4.0. The fix is available in these streams starting March 17, 2012 and can be obtained from:

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