Hibernate对JPA的支持

1.配置src/META-INF下persistence.xml注意文件名是固定的。

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <persistence xmlns="http://java.sun.com/xml/ns/persistence"
 3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4     xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
 5     http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">
 6     
 7     <persistence-unit name="hibPU" transaction-type="RESOURCE_LOCAL">
 8         <provider>org.hibernate.ejb.HibernatePersistence</provider>
 9           <properties>
10           <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/>
11             <property name = "hibernate.connection.driver_class" value = "com.mysql.jdbc.Driver"/>
12             <property name = "hibernate.connection.url" value = "jdbc:mysql://localhost:3306/hib"/>
13             <property name = "hibernate.connection.username" value = "root"/>
14             <property name = "hibernate.connection.password" value = "123456"/>
15             <property name = "hibernate.hbm2ddl.auto" value = "update"/>
16           <property name="hibernate.show_sql" value="true"/>
17           <property name="hibernate.format_sql" value="true"/>
18           </properties>
19     </persistence-unit>
20 
21 </persistence>

持久化单元的名称属性name是程序中引用的。provider的类所在的包必须有，否则报错。配置的属性名必须带hibernate前缀，如hibernate.dialect，否则报错。

hibernate.hbm2ddl.auto为update的意思是即便持久化类对应的表不存在，那么进行持久化操作时会创建表，如果存在则不创建。如果为create则每次加载都重新生成表。

2.持久化类可以采用注解方式配置映射，也可以采用xml文件的方式。如User.java对应User.hbm.xml放到与User的相同目录下，则即便在hibernate.cfg.xml中没有配置mapping resource，仍然有效。采用注解方式，可以不在hibernate.cfg.xml中配置mapping,如果要配置，则用<mapping class="com.tazi.domin.User"/>而不再是<mapping resource="com/tazi/domin/User.hbm.xml"/>.

 1 package com.tazi.domin;
 2 
 3 import javax.persistence.Column;
 4 import javax.persistence.Entity;
 5 import javax.persistence.GeneratedValue;
 6 import javax.persistence.GenerationType;
 7 import javax.persistence.Id;
 8 import javax.persistence.Table;
 9 
10 @Entity @Table(name="users")
11 public class User {
12     @Id
13     @GeneratedValue(strategy=GenerationType.IDENTITY)
14     private Integer id;
15     @Column
16     private String password;
17     //@Column 
18 //如果不加@Column则默认也会加上，除非使用@Transient
19     private String username;
20     public String getPassword() {
21         return password;
22     }
23     public void setPassword(String password) {
24         this.password = password;
25     }
26     public String getUsername() {
27         return username;
28     }
29     public void setUsername(String username) {
30         this.username = username;
31     }
32     public Integer getId() {
33         return id;
34     }
35     public void setId(Integer id) {
36         this.id = id;
37     }    
38 }

3.使用EntityManager操作数据

首先根据persistence-unit中的name创建实体管理器工厂。

 1         EntityManagerFactory emf=Persistence.createEntityManagerFactory("hibPU");
 2         EntityManager em=emf.createEntityManager();
 3         EntityTransaction tx=em.getTransaction();
 4         
 5         User user=new User();
 6         user.setUsername("tazi");
 7         user.setPassword("12345");
 8         tx.begin();
 9         em.persist(user);
10         tx.commit();
11         em.close();
12         emf.close();

输出：

1 Hibernate: 
2     insert 
3     into
4         users
5         (password, username) 
6     values
7         (?, ?)