Given the user is
    | firstname  | lastname  | nationality |
    | Roberto    | Lo Giacco | Italian     |

class User {
    String firstName;
    String lastName;
    Nationality nationality;
//getters / setters / etc
}

@Given("^the user is$")
 public void the_user_is(User user) {
     this.user = user;
 }

Type itemType = listItemType(type);
if (itemType == null) {
    throw new CucumberException("Not a Map or List type: " + type);
}

@Given("^the user is$")
 public void the_user_is(List<User> user) {
     this.user = user.get(0);
 }