Hi all, Thanks to Errai and his developers, i hope to have found in Errai the best solution to develop java REST web services (JAX-RS, implemented with Jersey and JAXB-RI on the server side) for GWT without to have to develop separate RPC services for the GWT front-end (i would like to have an UI agnostic solution for my webservices). But i have a problem with the unmarshalling of lists from JAXB annotated beans on the client side : i send a list of entities/beans ( like List<Customers> ) from my Jersey/JAX-RS service, in JSON, and it didn't work, the client side of the application trigger a NullPointerException when trying to unmarshall my List of customers. It looks like the array have not been well read by the underlying GWT JSON object (the value member is null). I had the same problem when sending only one entity ( like Customer ) from my webservice before i configure my custom JAXBContext on the server side to use a JSONConfiguration.natural() for JSON requests (so the numeric values were not enclosed by quotes (sending "id" : "30" instead of "id" : 30 for a numeric member of an entity was broking the JSON parser/unmarshaller on the GWT side). Actually, i have try to send back a CustomerContainer bean with a List<Customer> member but it also didn't work, for the same reason. So i was wondering if any of the users of Errai had/know the best configuration for the JSONConfiguration of Jersey to work with List of beans* and would like to share it ? Does anybody succeed to interface the 2 differents APIs ? Sorry to bother you with this but i thought i should ask before spending one more day on this ! :-) Thanks in advance for any answer, Best regards, Ludo * ideally if it could works well with @XmlID and @XmlIDRef, it would be really fine - i have now make the members like this @XmlTransient so they didn't encumber the objects graph, but it still didn't work for lists of basic objects without complex dependencies.