Question

I’m using JAXB to read and write XML. What I want is to use a base JAXB class for marshalling and an inherited JAXB class for unmarshalling. This is to allow a sender Java application to send XML to another receiver Java application. The sender and receiver will share a common JAXB library. I want the receiver to unmarshall the XML into a receiver specific JAXB class which extends the generic JAXB class.

Example:

This is the common JAXB class which is used by the sender.

@XmlRootElement(name='person') public class Person {     public String name;     public int age; } 

This is the receiver specific JAXB class used when unmarshalling the XML. The receiver class has logic specific to the receiver application.

@XmlRootElement(name='person') public class ReceiverPerson extends Person {     public doReceiverSpecificStuff() ... } 

Marshalling works as expected. The problem is with unmarshalling, it still unmarshals to Person despite the JAXBContext using the package name of the subclassed ReceiverPerson.

JAXBContext jaxbContext = JAXBContext.newInstance(package name of ReceiverPerson); 

What I want is to unmarshall to ReceiverPerson. The only way I’ve been able to do this is to remove @XmlRootElement from Person. Unfortunately doing this prevents Person from being marshaled. It’s as if JAXB starts at the base class and works its way down until it finds the first @XmlRootElement with the appropriate name. I’ve tried adding a createPerson() method which returns ReceiverPerson to ObjectFactory but that doesn’t help.

Answer 1

You’re using JAXB 2.0 right? (since JDK6)

There is a class:

javax.xml.bind.annotation.adapters.XmlAdapter<ValueType,BoundType> 

which one can subclass, and override following methods:

public abstract BoundType unmarshal(ValueType v) throws Exception; public abstract ValueType marshal(BoundType v) throws Exception; 

Example:

public class YourNiceAdapter         extends XmlAdapter<ReceiverPerson,Person>{      @Override public Person unmarshal(ReceiverPerson v){         return v;     }     @Override public ReceiverPerson marshal(Person v){         return new ReceiverPerson(v); // you must provide such c-tor     } } 

Usage is done by as following:

@Your_favorite_JAXB_Annotations_Go_Here class SomeClass{     @XmlJavaTypeAdapter(YourNiceAdapter.class)     Person hello; // field to unmarshal } 

I’m pretty sure, by using this concept you can control the marshalling/unmarshalling process by yourself (including the choice the correct [sub|super]type to construct).