JAXB and Unmapped Properties

JAXB (JSR-222) is configuration by exception, meaning that there is a default mapping applied to domain objects. This means that sometimes you need to explicitly exclude a field/property. In this post I’ll discuss how this can be done using @XmlTransient or @XmlAccessorType(XmlAccessType.NONE) and when each option is appropriate.

@XmlTransient

When you mark a field/property with @XmlTransient you are explicitly telling your JAXB implementation to treat it as an unmapped property. This is useful when less than half of the fields/properties are unmapped.

package blog.unmapped;
 
import java.util.List;
import javax.xml.bind.annotation.*;
 
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
    @XmlTransient
    private int id;
 
    private String firstName;
 
    private String lastName;
 
    private Address billingAddress;
 
    private Address shippingAddress;
 
    private List<PhoneNumber> phoneNumbers;
 
}

If more than half of the fields/properties are unmapped then we stop gaining the benefit of configuration by exception since we need to do more work to exclude properties with @XmlTransient than we would have had to do to map the mapped properties. Next I’ll demonstrate how we can leverage @XmlAccessorType(XmlAccessType.NONE) for this use case.

package blog.unmapped;
 
import java.util.List;
import javax.xml.bind.annotation.*;
 
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
    @XmlTransient
    private int id;
 
    private String firstName;
 
    private String lastName;
 
    @XmlTransient
    private Address billingAddress;
 
    @XmlTransient
    private Address shippingAddress;
 
    @XmlTransient
    private List<PhoneNumber> phoneNumbers;
 
}

@XmlAccessorType(XmlAccessType.NONE)

By setting @XmlAccessorType(XmlAccessType.NONE) we are disabling configuration by exception. Now only explicitly mapped properties will be mapped. This is useful when less than half of the fields/properties of a domain object are mapped.

package blog.unmapped;
 
import java.util.List;
import javax.xml.bind.annotation.*;
 
@XmlAccessorType(XmlAccessType.FIELD)
public class Customer {
 
    @XmlTransient
    private int id;
 
    private String firstName;
 
    private String lastName;
 
    @XmlTransient
    private Address billingAddress;
 
    @XmlTransient
    private Address shippingAddress;
 
    @XmlTransient
    private List<PhoneNumber> phoneNumbers;
 
}

Further Reading

If you enjoyed this post then you also like:

• Using JAXB’s @XmlAccessorType to Configure Field or Property Access 
• Ignoring Inheritance with @XmlTransient

Reference: JAXB and Unmapped Properties from our JCG partner Blaise Doughan at the Java XML & JSON Binding blog.