@PrePersist
public void prePersist() {
    updatedAt = new Timestamp(System.currentTimeMillis());
    createdAt = new Timestamp(System.currentTimeMillis());
}

/**
 * 在持久化时，数据有变化，此方法会执行
 */
@PreUpdate
public void preUpdate() {
    updatedAt = new Timestamp(System.currentTimeMillis());
}

@PrePersist