Hibernate Annotations 实战介绍

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)

　

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