hibernate+mysql，注解方式，自动添加创建，更新时间

hibernate+mysql，自动添加创建，更新时间：

package com.springhibernate.dxt;


import java.util.Date;


import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;


import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;


@Entity
@Table(name = "users")
public class User {
    @Id  
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(length = 20)
    private int    id;


    @Column(length = 120)
    private String username;