title: Json DateTime object to GregorianCalendar
body: <p>I have a Mapping Problem using jackson library to convert a Json API callback to a custom Object.</p>
  
  <p>I've got my User custom class :</p>
  
  <pre><code>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&lt;String, Object&gt; 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");
      }
  }
  </code></pre>
  
  <p>Here's my callback :</p>
  
  <pre><code>{
      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
      }
  }
  </code></pre>
  
  <p>Then, I try to init a User object :</p>
  
  <pre><code>// 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"])
  </code></pre>
  
  <p>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 ?</p>