[
  {
  "fullName": "a",
  "password": "a",
    "roles": [
      {
       "role_id": "dilbert"
      },
       {
       "roleId": "admin"
      }
      ]
  }
]

public static User fromJson(JSONObject json) throws JSONException {
        User u = new User();
        u.setFullName(json.getString("fullName"));
        u.setPassword(json.getString("password"));

        JSONArray array = json.getJSONArray("roles");
        for(int i=0; i < array.length(); i++){
            JSONObject o = array.getJSONObject(i);
            Role r = Role.fromJson(o);

        }

        return u;
    }

public static Role fromJson(JSONObject json) throws JSONException {
        Role r = new Role();
        r.setRole_id(json.getString("roles"));
        return r;
    }