JPA:createNativeQuery.getSingleResult()返回一个对象,如何在该对象中获取一个属性的值

public class User {
    private int id;
    private String username;

    // 构造函数、getter和setter方法

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

EntityManager entityManager = getEntityManager();
String sql = "SELECT id, username FROM user WHERE id = 1";
TypedQuery<User> query = entityManager.createNativeQuery(sql, User.class);
User user = query.getSingleResult();

String username = user.getUsername();
System.out.println("Username: " + username);