Java: Serialize a Collection XML

Question

Every time I've searched for something on how to serialize to XML, I found the bean serializers. It seems that everything has to be declared as a property, which defeats my purpose. I want to serialize complex hierarchies (until they get to primitives, of course) in XML, start with (say) a Dictionary or List as the parent object.

What options are there for automatic XML serialization?

I found some references to JAXB from 2004, is that still the way to go?

Answer 1

Try the XStream library. It will easily serialize any complex object hierarchy you can throw at it.

Answer 2

I've had a lot of success with JAXB, especially when using the support for it in NetBeans. I know for a fact it supports lists. I haven't tried it with maps, but I suspect it works. If nothing else, just make a simple bean that contains the list and let that be the serialized bean.

Answer 3

You can use the standard java.bean.XMLEncoder / Decoder classes to serialize collections because the mechanism allows for the calling of methods via XML. The output looks something like:

<object class="java.util.ArrayList">
  <void method="add">
    <string>Hello</string>
  </void>
  <void method="add">
    <string>World</string>
  </void>
</object>

Of course this has weaknesses; for example you cannot easily serialize a Collections.emptyXXXX() but there are workarounds. But because everything works according to the publicly-supported API of the classes, the persistent XML form is resilient to schema changes.

I've found it a very useful persistent mechanism for Java objects.