每次自动更新JPA时间戳的策略是什么？@H_404_2@这个实体改变了？

如果我还想要一个“创建”时间戳,那么我该怎么办？只有当实体第一次被持久化时才设置,再也不能再被修改了？

@Entity
 public class Item implements Serializable {
     private static final long serialVersionUID = 1L;
     private Integer id;
     private String note;


    public Item () {
    }


    @Id
    @GeneratedValue(strategy=SEQUENCE)
    @Column(unique=true,nullable=false)
    public Integer getId() {
        return this.id;
    }

    public void setId(Integer id) {
        this.id = id;
    }


    @Column(length=255)
    @Column(nullable=false)
    public String getNote() {
        return this.note;
    }

    public void setNote(String note) {
        this.note = note;
    }

    @Column(nullable=false)
    public Timestamp getUpdated() {
        return this.updated;
    }

    public void setUpdated(Timestamp updated) {
        this.updated = updated;
    }


}