XOM API for Processing XML with Java

[Wolfgang Hoschek <whoschek AT lbl.gov>]

> > The people asking for Java serialization probably don't really care about
> > the above argument.  They just want to use XOM as the XML package in an
> > application that *requires* Java serialization (eg. EJB).
> >
> > It appears that saying "XOM won't be serializable" is equivalent to saying
> > "XOM can't be used in EJB".  This is perhaps a reasonable thing to say,
> > perhaps not, but it's almost entirely orthogonal to a discussion of which
> > serialization method is "better".
>
> That's been said. I've yet to be convinced that statement is true 
> though. I don't know enough about EJB to judge whether "EJB requires 
> object serialization" is actually a true statement for myself. To 
> convince me, you're going to need a compelling use case, and an EJB 
> expert who confirms that that use-case really does need XOM objects 
> to be Serializable. For instance, you'll need to explain to me why 
> you can't just call toXML and serialize the resulting string. Hell, 
> you coudl even do this in your own subclass that implemented 
> Serializable and provided readObject and writeObject methods (or 
> would it have to implement Externalizable for complete control? I 
> forget.) Either way, that seems like a simple fix for any system that 
> simple doesn't work with serializing XOM objects.
>
> If good reasons were provided, then I would begin to consider whether 
> implementing Serializable was practical. It may not be. But so far, I 
> remain unconvinced it's even useful.

Implementing Java serialization so that it works for long term 
persistence across xom versions and jdk versions (even across different 
javac's) is complex, fragile, a pain in the ass and IMHO not worth it.

But people that want/need java serialization typically do not want that 
anyway (if they'd need it then relational dbs, xml serialization etc. 
are much better options). Such people typically work in tightly coupled 
scenarios like the ones outlined by others here before, where versions 
and upgrades are under control and the same everywhere in their 
application. Implementing that kind of restricted java serialization is 
easy: Just add "implements Serializable" to all relevant and dependent 
classes. If you document in xom that nothing more than that restricted 
notion of serializable is guaranteed, you should be fine.

This seems a useful compromise to me.

Wolfgang.