How can you use GWT AutoBeans to parse a JSON message when some of the return values could be an object or a collection of objects?

Question

Is it possible to parse a JSON message using GWT AutoBeans when one of the objects returned may be a collection but not always?

For example, if I have a JSON message returning an author and his/her associated writings, it's possible that there could be zero or more books being returned.

{ "name" : "William Gibson", "books" : { bookname : "Neuromancer" } }

could be one response, but so could this:

{ "name" : "William Gibson", "books" : [ { bookname: "Neuromancer"}, { bookname : "Pattern Recognition" } ] }

When I attempt to model this with an interface to be used for marshalling with an AutoBean, I get "expecting indexed data" errors if only one book is returned.

Interface for the AutoBean:

public interface Author {
  @PropertyName(value="name")
  String getAuthorName();
  @PropertyName(value="book")
  List<String> getBooks();
}

Snippet of error:

java.lang.AssertionError: Expecting indexed data
at com.google.web.bindery.autobean.shared.impl.SplittableList.<init>(SplittableList.java:64)

Is this not possible with AutoBeans?

(Note: using GWT 2.5.0 GA)

Answer 1

If you have a List, AutoBeans expects a JSON array. That array could contain zero, one or more elements, but it has to be an array (or be absent).

I think you can make your getBooks method return a Splittable though. You could then know whether it's an array (isIndexed()) or not. If you need the array to contain objects, you'd then have to iterate on the array (size() and get(int)) and pass each element to AutoBeanCodex.decode() to decode them (or directly pass the splittable if it's not an array).