今天有时间大体看了一下Hibernate Annotations,决定放弃xdoclet生成hbm的想法，开始学习annotation.
首先大体的来看一下：
一：Class Level:
1:通过@Entity声明当前pojo为实体Bean
2:通过@Table定义对应数据库表的属性
name：表名，默认实体类名
uniqueConstraints：定义表的唯一性约束
例：定义表名为tb_user,并且用户名唯一，不能重复
@Entity
@Table(
name = "tb_user",
uniqueConstraints =
{@UniqueConstraint(columnNames = "userName")}
)
public class User implements Serializable {
private Integer id;
private String userName;
}二：Method Level:
@Basic
@Transient
@Column
所有非static非transient都会被持久化，也就是说所有加@Transient是不会被保存到数据库中的，所有没有加注的默认为@Basic,通过Column我们可以更一步的定义列名，是否为空，长度，是否可更新等等属性值，
例：
@Column(name = "userName", nullable = false, length = 80, unique = true)
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
@Transient
public String getPassword() {
return password;
} 默认的列名就是属性名，上面的name="userName"只是演示而已。
password加注为@Transient，所以通过SchemaExport导入Schema，查看表结构是没有这个字段的。
@Temporal
日期类型，分三种，Time,Date,Timestamp
例：
@Temporal(TemporalType.TIMESTAMP)
public Date getBirthday() {
return birthday;
} @Lob
1:所有的Clob，
Character，char，String都会被转为Clob
2:所有的Blob，Byte[]，byte[]，serializable都会被转为Blob
例：
@Lob
public Clob getResume() {
return resume;
}
@Lob
public Blob getImage() {
return image;
}
@Id
就是标识了，暂时还没有详读文档，看了一下test
最简单方式如下：
@Id
@GeneratedValue
public String getId() {
return id;
} 我看了一下mysql生成的sql
id integer not null auto_increment,
primary key (id), 应该是hibernate根据数据库类型自动选择的(说了一句废话
)，我猜是生成方式native
当然我们可以根据我们需要选择其他的生成方式，例如常用的uuid
@Id
@GeneratedValue(generator = "system-uuid")
@GenericGenerator(name = "system-uuid", strategy = "uuid")
public Integer getId() {
return id;
} @Version
乐观锁
三：跑起来
和Hibernate官方网站一样，来个HibernateUtil
/**
* @author martin
*/
public class HibernateUtil {
private static final SessionFactory sessionFactory;
static {
AnnotationConfiguration cfg =
new AnnotationConfiguration().addAnnotatedClass(User.class);
new SchemaExport(cfg).execute(true, true, false, true);
sessionFactory = cfg.buildSessionFactory();
}
public static Session getSession() {
return sessionFactory.openSession();
}
}
注意这里的
new AnnotationConfiguration()！
Test:
/**
* @author martin
*/
public class HibernateUtilTest extends TestCase {
public void testAddUser() {
User user = new User();
user.setUserName("martin");
save(user);
assertNotNull(user.getId());
}
public void testUpdateUser() {
Session session = HibernateUtil.getSession();
Query query =
session.createQuery("from User as user where user.userName=:name");
query.setParameter("name", "martin");
List list = query.list();
session.close();
assertEquals(1, list.size());
User user = (User) list.get(0);
user.setUserName("martin xus");
save(user);
assertEquals(new Integer(1), user.getVersion());
}
private void save(User user) {
Session session = HibernateUtil.getSession();
Transaction tx = session.beginTransaction();
session.saveOrUpdate(user);
session.flush();
tx.commit();
session.close();
}
}
创建的表结构为：
create table tb_user (
id varchar(32) not null,
birthday datetime,
resume text,
image blob,
optlock integer,
password varchar(255),
userName varchar(80) not null unique,
primary key (id),
unique (userName)
) 完整User代码(省掉了所有属性的setter)：
import org.hibernate.annotations.GenericGenerator;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Date;
import java.sql.Clob;
import java.sql.Blob;
/** *//**
* @author martin
*/
@Entity
@Table(
name = "tb_user",
uniqueConstraints =
{@UniqueConstraint(columnNames = "userName")}
)
public class User implements Serializable {
private String id;
private String userName;
private String password;
private Date birthday;
private Clob resume;
private Blob image;
private Integer version;
@Id
@GeneratedValue(generator = "system-uuid")
@GenericGenerator(name = "system-uuid", strategy = "uuid")
@Column(length = 32)
public String getId() {
return id;
}
@Column(nullable = false, length = 80, unique = true)
public String getUserName() {
return userName;
}
public String getPassword() {
return password;
}
@Temporal(TemporalType.TIMESTAMP)
public Date getBirthday() {
return birthday;
}
@Version
@Column(name = "optlock")
public Integer getVersion() {
return version;
}
@Lob
public Clob getResume() {
return resume;
}
@Lob
public Blob getImage() {
return image;
}
//setter
} 四：next,明天的学习计划.
参考
Hibernate Annotations Refrence