XStream and default field values.

Hello everyone.

Is there anyway to tell XStream to treat missing elements as empty
elements? Or, even better, let corresponding fields keep their value
from object initialization?

My explanation on why this would be useful follows.

I'm using XStream to deserialize a Java object. The XML format is
actually a published interface (at least internally) which can evolve
slowly over time.

The XStream process is replacing a Spring Binding process, and we have a
lot of framework/library code that makes certain assumptions about the
bean contents/structure. One of the assumptions is that certain
properties are not null, even if they are optional. XStream seems to be
setting the fields (which are currently final) to null, if there isn't a
corresponding value in the XML. This means that all processed XML will
need to have the optional elements present, or it will cause problems.

for example:
// Foo.java
import java.io.Serializable;
public class Foo implements Serializable {
    private final Bar bar = new Bar;
    private String myString;

    public void doSomething() {
        bar.doSomething();
    }
}

// Bar.java
import java.io.Serializable;
public class Bar implements Serializable {
   public void doSomething() {
      System.out.println("Working!");
   }
}

// Main.java
public class Main {
    private static String xml =
"<foo>" +
   "<myString>This is the value of myString!</myString>" +
"</foo>";

    public static void main(String...args) {
       XStream xStream = new XStream();
       xStream.aliasType("foo", Foo.class);
       Foo foo = (Foo)xStream.fromXML(xml);
       foo.doSomething(); // NPE for bar.doSomething();
    }
}

--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>