Best practice: Java/XML serialization: how to determine to what class to deserialize?

Question

I have an application that saves its context to XML. In this application, there is a hierarchy of classes, that all implement a common interface, and that represent different settings. For instance, a first setting class may be made of 4 public float fields, another one can be made of a sole HashMap.

I am trying to determine what is the best way to handle writing and reading to XML in a generic way. I read on this site a lot about JAXB and XStream for instance, which are able to make a specific class instance from XML.

However my question is related to the fact that the actual class can be anything that implement a given interface. When you read the XML file, how would you guess the actual class to instantiate from the XML data? How do you do that in your applications?

I thought that I could write the .class name in a XML attribute, read it and compare it to all possible class .class names, until I find a match. Is there a more sensible way?

Thanks

Answer 1

In my case I just have a kind of header that stores the class name that is serialized and when de-serializing it I just use the header value to figure out to which class shall I de-serialize the values.

Answer 2

xstream should already take care of this and create the object of correct type.

The tutorial seems to confirm that:

To reconstruct an object, purely from the XML:

Person newJoe = (Person)xstream.fromXML(xml);

If you don't know the type, you will have to first assign it to the common interface type:

CommonInterface newObject = (CommonInterface)xstream.fromXML(xml);
// now you can either check its type or call virtual methods

Answer 3

A best practice would to use an established, well documented XML parser/mapper. All of the serialization/deserialization work has been done, so you can worry about your business logic instead. Castor and Apache Axiom are two APIs that I have used to marshal/unmarshall(serialize/deserialize) Java Classes and XML.
http://www.castor.org

Apache Axiom