从 hbm.xml 到 Annotations
下面让我们先看一个通常用 hbm.xml 映射文件的例子. 有3个类 .HibernateUtil.java 也就是 Hibernate文档中推荐的工具类,Person.java, Test.java 测试用的类.都在test.hibernate 包中. 每个类的代码如下:
HibernateUtil:
01 package test.hibernate;
02
03 import org.hibernate.HibernateException;
04 import org.hibernate.Session;
05 import org.hibernate.SessionFactory;
06 import org.hibernate.cfg.Configuration;
07
08 public class HibernateUtil {
09 public static final SessionFactory sessionFactory;
10
11 static {
12 try {
13 sessionFactory = new Configuration()
14 .configure()
15 .buildSessionFactory();
16 } catch (HibernateException e) {
17 // TODO Auto-generated catch block
18
19 e.printStackTrace();
20 throw new ExceptionInInitializerError(e);
21 }
22 }
23
24 public static final ThreadLocal<Session> session = new ThreadLocal<Session>();
25
26 public static Session currentSession() throws HibernateException {
27 Session s = session.get();
28
29 if(s == null) {
30 s = sessionFactory.openSession();
31 session.set(s);
32 }
33
34 return s;
35 }
36
37 public static void closeSession() throws HibernateException {
38 Session s = session.get();
39 if(s != null) {
40 s.close();
41 }
42 session.set(null);
43 }
44 }
Person:
01 package test.hibernate;
02
03 import java.util.LinkedList;
04 import java.util.List;
05
06 /**
07 *
08 */
09
10 @SuppressWarnings("serial")
11 public class Person implements java.io.Serializable {
12
13 // Fields
14
15 private Integer id;
16
17 private String name;
18
19 private String sex;
20
21 private Integer age;
22
23 private List list = new LinkedList();
24
25 // Collection accessors
26
27 public List getList() {
28 return list;
29 }
30
31 public void setList(List list) {
32 this.list = list;
33 }
34
35 /** default constructor */
36 public Person() {
37 }
38
39 /** constructor with id */
40 public Person(Integer id) {
41 this.id = id;
42 }
43
44 // Property accessors
45
46 public Integer getId() {
47 return this.id;
48 }
49
50 public void setId(Integer id) {
51 this.id = id;
52 }
53
54 public String getName() {
55 return this.name;
56 }
57
58 public void setName(String name) {
59 this.name = name;
60 }
61
62 public String getSex() {
63 return this.sex;
64 }
65
66 public void setSex(String sex) {
67 this.sex = sex;
68 }
69
70 public Integer getAge() {
71 return this.age;
72 }
73
74 public void setAge(Integer age) {
75 this.age = age;
76 }
77
78 }
Test:
01 /*
02 * Created on
03 * @author
04 */
05 package test.hibernate;
06
07 import java.sql.SQLException;
08
09 import org.hibernate.FlushMode;
10 import org.hibernate.HibernateException;
11 import org.hibernate.Session;
12 import org.hibernate.Transaction;
13
14 public class Test {
15
16 public static void main(String [] args) {
17 Session s = HibernateUtil.currentSession();
18
19 Transaction tx = s.beginTransaction();
20
21 // Person p = (Person) s.load(Person.class, 1);
22 // System.out.println(p.getName());
23 Person p = new Person();
24
25 p.setAge(19);
26 p.setName("icerain");
27 p.setSex("male");
28 s.save(p);
29 s.flush();
30 /*
31 Person p2 = (Person) s.get(Person.class, new Integer(1));
32 System.out.println(p2.getName());
33 p2.setName("ice..");
34 s.saveOrUpdate(p2);
35 s.flush();
36 Person p3 = (Person) s.get(Person.class, new Integer(2));
37 System.out.println(p3.getName());
38 s.delete(p3);
39 */
40
41 tx.commit();
42 try {
43 System.out.println(p.getName());
44 } catch (Exception e) {
45 // TODO Auto-generated catch block
46 e.printStackTrace();
47 }
48
49 HibernateUtil.closeSession();
50 }
51 }
hibernate.cfg.xml 配置文件如下,利用mysql 数据库.
<?xml version="1.0" encoding="UTF-8"?>
<hibernate-configuration>
<session-factory>
<property name="hibernate.connection.driver_class">org.gjt.mm.mysql.Driver</property>
<property name="hibernate.connection.password">你的数据库密码</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost/数据库名</property>
<property name="hibernate.connection.username">用户名</property>
<property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="show_sql">true</property>
<property name="hibernate.transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property>
<property name="hibernate.transaction.auto_close_session">false</property>
<property name="hibernate.hbm2ddl.auto">update</property>
<mapping resource="test/hibernate/annotation/Person.hbm.xml"/>
</session-factory>
</hibernate-configuration>
其中 配置了<property name="hibernate.hbm2ddl.auto">update</property>属性 自动导入数据库ddl.生产的ddl sql语句如下
create table person (id integer not null auto_increment, name varchar(255), sex varchar(255), age integer, person integer, primary key (id))
alter table person add index FKC4E39B5511C4A5C2 (person), add constraint FKC4E39B5511C4A5C2 foreign key (person) references person (id)
而Person.hbm.xml 文件如下:
<?xml version="1.0"?>
<hibernate-mapping>
<class name="test.hibernate.Person" table="person">
<id name="id" type="integer">
<column name="id" />
<generator class="native"></generator>
</id>
<property name="name" type="string">
<column name="name" />
</property>
<property name="sex" type="string">
<column name="sex" />
</property>
<property name="age" type="integer">
<column name="age" />
</property>
<bag name="list" cascade="all">
<key column="person"></key>
<one-to-many class="test.hibernate.Person"/>
</bag>
</class>
</hibernate-mapping>
下面让我们看看利用 Hibernate Annotations 如何做,只要三个类 不再需要 hbm.xml配置文件:
还要把用到的两个jar文件 放入的类路径中. 具体如何做,请参考 Hibernate Annotations 中文文档
http://hibernate.6644.net
HibernateUtil.java 也就是 Hibernate文档中推荐的工具类,Person.java 一个持久化的类, Test.java 测试用的类.都在test.hibernate.annotation 包中. 每个类的代码如下:
HibernateUtil
01 package test.hibernate.annotation;
02
03 import org.hibernate.HibernateException;
04 import org.hibernate.Session;
05 import org.hibernate.SessionFactory;
06 import org.hibernate.cfg.AnnotationConfiguration;
07 import org.hibernate.cfg.Configuration;
08
09 public class HibernateUtil {
10 public static final SessionFactory sessionFactory;
11
12 static {
13 try {
14 sessionFactory = new AnnotationConfiguration() //注意: 建立 SessionFactory于前面的不同
15 .addPackage("test.hibernate.annotation")
16 .addAnnotatedClass(Person.class)
17
18 .configure()
19 .buildSessionFactory();
20 //new Configuration().configure().buildSessionFactory();
21 } catch (HibernateException e) {
22 // TODO Auto-generated catch block
23
24 e.printStackTrace();
25 throw new ExceptionInInitializerError(e);
26 }
27 }
28
29 public static final ThreadLocal<Session> session = new ThreadLocal<Session>();
30
31 public static Session currentSession() throws HibernateException {
32 Session s = session.get();
33
34 if(s == null) {
35 s = sessionFactory.openSession();
36 session.set(s);
37 }
38
39 return s;
40 }
41
42 public static void closeSession() throws HibernateException {
43 Session s = session.get();
44 if(s != null) {
45 s.close();
46 }
47 session.set(null);
48 }
49 }
Person:
01 package test.hibernate.annotation;
02
03 import java.util.LinkedList;
04 import java.util.List;
05
06 import javax.persistence.AccessType;
07 import javax.persistence.Basic;
08 import javax.persistence.Entity;
09 import javax.persistence.GeneratorType;
10 import javax.persistence.Id;
11 import javax.persistence.OneToMany;
12 import javax.persistence.Table;
13 import javax.persistence.Transient;
14
15 /**
16 *
17 */
18
19 @SuppressWarnings("serial")
20 @Entity(access = AccessType.PROPERTY) //定义该类为实体类
21 @Table //映射表
22 public class Person implements java.io.Serializable {
23
24 // Fields
25
26 private Integer id;
27
28 private String name;
29
30 private String sex;
31
32 private Integer age;
33
34 private List list = new LinkedList();
35
36 // Constructors
37 /** default constructor */
38 public Person() {
39 }
40
41 /** constructor with id */
42 public Person(Integer id) {
43 this.id = id;
44 }
45
46 // Property accessors
47 @Id
48 public Integer getId() {
49 return this.id;
50 }
51
52 public void setId(Integer id) {
53 this.id = id;
54 }
55
56 @Basic
57 public String getName() {
58 return this.name;
59 }
60
61 public void setName(String name) {
62 this.name = name;
63 }
64
65 @Basic
66 public String getSex() {
67 return this.sex;
68 }
69
70 public void setSex(String sex) {
71 this.sex = sex;
72 }
73
74 @Basic
75 public Integer getAge() {
76 return this.age;
77 }
78
79 public void setAge(Integer age) {
80 this.age = age;
81 }
82 @Transient //由于本例不打算演示集合映射 所有声明该属性为 Transient
83 public List getList() {
84 return list;
85 }
86
87 public void setList(List list) {
88 this.list = list;
89 }
90
91 }
注意该实体类中的属性都使用了默认值.
Test.java 代码同上
不需要了 hbm.xml 映射文件, 是不是简单了一些 .给人认为简化了一些不是主要目的.主要是可以了解一下 EJB3 的持久化机制 ,提高一下开发效率才是重要的.
好了 .本例就完了 . 感觉怎么样了 .欢迎你来批批.
PS:
生成的数据库表 和 程序执行后的 数据库情况如下
mysql> describe person;
+--------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(255) | YES | | NULL | |
| sex | varchar(255) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| person | int(11) | YES | MUL | NULL | |
+--------+--------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> select * from person;
+----+---------+------+------+--------+
| id | name | sex | age | person |
+----+---------+------+------+--------+
| 1 | icerain | male | 19 | NULL |
+----+---------+------+------+--------+
1 row in set (0.03 sec)
