XML unmarshalling using JAXB, with field type based on XML attribute value?

Question

My application receives, from another application, xml of the form:

<targetedMessage>
    <sender>the sender</sender>
    <payload class="other.app.classpath.Foo">
        <id>1</id>
    </payload>
</targetedMessage>

where Foo is any one of several classes which exist in both my module and the other application, and implements a common interface:

@XmlAccessorType(value = XmlAccessType.FIELD)
@XmlRootElement
public class Foo implements MyInterface {
    private long id;
    \\ getters and setters
}

and the TargetedMessage class is:

@XmlAccessorType(value = XmlAccessType.FIELD)
@XmlRootElement
public class TargetedMessage {
    private String sender;
    private MyInterface payload;
    \\ getters and setters
}

I have an enum which maps the other apps class-paths to their classes in my module:

public enum MyClasses {
    FOO(Foo.class, "other.app.classpath.Foo"),
    BAR(Bar.class, "other.app.classpath.Bar"),
    \\ ...
}

Using JAXB, is it possible to unmarshal the xml so that the payload is of the correct type (in the above case, the payload class would be Foo).

It's possible, but you'll need to define a class that can contain the content of any of your MyInterface implementations. I don't feel like writing an answer, so see https://dzone.com/articles/jaxb-and-inhertiance-using — kumesana, Jun 27 '18 at 13:51

score 0 · Answer 1 · answered Jun 28 '18 at 17:34

I don't know about JAXB but SimpleXml can do it:

@XmlName("targetedMessage")
public class TargetedMessage {
    String sender;
    @XmlAbstactClass(attribute="class", types={
        @TypeMap(name="other.app.classpath.Foo", type=Foo.class),
        @TypeMap(name="other.app.classpath.Bar", type=Bar.class)
    })
    Payload payload;
}
interface Payload {}
public class Foo implements Payload {
    Integer id;
}
public class Bar implements Payload {
    String name;
}

final String data = ...

final SimpleXml simple = new SimpleXml();
final TargetedMessage message = simple.fromXml(data, TargetedMessage.class);
System.out.println(message.payload.getClass().getSimpleName());
System.out.println(((Foo)message.payload).id);

Will output:

Foo
1

From maven central:

<dependency>
    <groupId>com.github.codemonstur</groupId>
    <artifactId>simplexml</artifactId>
    <version>1.5.0</version>
</dependency>

XML unmarshalling using JAXB, with field type based on XML attribute value?

1 Answers1