Is using default method in an interface a good pattern to avoid code duplications? - interface

Question

We have a lot of code duplication in data holder classes that can be serialized to a XML string:
public String toXml() throws JAXBException {
final JAXBContext context = JAXBContext.newInstance(this.getClass());
final Marshaller marshaller = context.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
final StringWriter stringWriter = new StringWriter();
marshaller.marshal(this, stringWriter);
return stringWriter.toString();
}
Why not move this code to a single interface with default implementation? So a simple implements ToXmlUtf8 would be enough to share the default implementation and avoid code duplicates:
public interface ToXml {
default String toXml() throws JAXBException {
final JAXBContext context = JAXBContext.newInstance(this.getClass());
final Marshaller marshaller = context.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");
final StringWriter stringWriter = new StringWriter();
marshaller.marshal(this, stringWriter);
return stringWriter.toString();
}
}
Has anybody done this before successfully?
Other solutions?
I could also imagine using an annotation to generate this code.
Are there any ready to use solutions available?

Answer 1

Yes, default methods can be used in that way.
Although the intended use case of default methods is adding new functionality to existing interfaces without breaking old code, default methods have other uses as well. Default methods are also used in interfaces which were added in Java 8, such as in java.util.Predicate, so even the Java designers recognized that adding new functionality to existing interfaces is not the only valid use of default methods.
A disadvantage could be that the implemented interfaces are part of a class's public contract, but in your case this does not seem to be a problem.

Answer 2

If you're using the exact same method then an interface won't help, what you want to do is make a static method and put that in a util class