Json DateTime object to GregorianCalendar
===

I have a Mapping Problem using jackson library to convert a Json API callback to a custom Object.

I've got my User custom class :

    public class User {
        protected String id;
        protected GregorianCalendar registredAt;
        protected String username;
        protected Team team;
        
        public User() {
            
        }
        
        public User(String id, GregorianCalendar registredAt, String username, Team team) {
            this.id = id;
            this.registredAt = registredAt;
            this.username = username;
            this.team = team;
        }
        	
        public User(HashMap<String, Object> attributes) {
            this.id = (String) attributes.get("id");
            this.registredAt = (GregorianCalendar) attributes.get("registredAt");
            this.username = (String) attributes.get("username");
            this.team = (Team) attributes.get("team");
        }
    }

Here's my callback :

    {
        id: "4feab37c5600bbd56f000132",
        registredAt: {
            date: "2012-06-27 09:17:15",
            timezone_type: 3,
            timezone: "Europe/Paris"
        },
        username: "John Doe",
        team: {
            id: "4feab37c5600bbd56f000130",
            indice: 1,
            name: "John Doe's Team",
            score: 200
        }
    }

Then, I try to init a User object :

    // Code from a doInBackground() method of a custom AsyncTask.
    URL completePath = new URL(apiBaseURL + "api/user/4feab37c5600bbd56f000132/show");
    APIconnection = (HttpURLConnection) completePath.openConnection();
    APIconnection.setDoInput(true);
    APIconnection.connect();
    callbackParser = jsonFactory.createJsonParser(APIconnection.getInputStream());
    response = objectMapper.readValue(callbackParser, User.class);
    // Catch a JsonMappingException :
    Can not deserialize instance of java.util.Calendar out of START_OBJECT token at [Source: org.apache.harmony.luni.internal.net.www.protocol.http.FixedLengthInputStream@4082c7a0; line: 1, column: 33] (through reference chain: classes.models.User["registredAt"])


I think the problem is that the callback registredAt object is a json_encoded PHP \DateTime instance...
Should I change the type of the registredAt Java User object ?
Or does something is missing in my constructor ?