Rewrite code of ModsExporter

[koppor]

The class org.jabref.logic.exporter.ModsExporter uses JAXB, but can be rewritten using a StAX-Writer and thus getting rid of a JAXB dependency. (Please also set the correct namespaces!).

Example:

Old code:

    JAXBElement<ModsCollectionDefinition> jaxbElement = new JAXBElement<>(
                    new QName(MODS_NAMESPACE_URI, "modsCollection"), ModsCollectionDefinition.class, modsCollection);

New code:

            writer.writeStartDocument("utf-8", "1.0");
            writer.writeStartElement(MODS_NAMESPACE_URI, "modsCollection");
            ... export of ModsCoillectionDefinition ...
            writer.writeEndElement();
            writer.writeEndDocument();

Similar to #9673, the gradle build target generateModsSource can be removed and the xsd file be removed from the source repository.

[yenniejunvu]

Hi! I am a uni student and would like to attempt this.

[ThiloteE]

This is actually a much needed change, as we are currently struggling with having too many dependencies and scratching the limit. Thank you for choosing this issue!

[yenniejunvu]

I am glad to be of assistance. I am not very familiar with either JAXB or StAX, so I am reading some documentation to familiarize myself. Other than that, are there other pointers on where to begin for this task?

[Siedlerchr]

Just look at the other implementations that have been already converted

[koppor]

The deep link to the changed code is at #9673.

Together with the PR, the howto linked at https://mkyong.com/java/how-to-write-xml-file-in-java-stax-writer/ should be enough to get started.