使用Hibernate EntityManager（摘自hibernate实战第二版）

     Hibernate EntityManager是围绕提供JPA编程接口的Hibernate Core的一个包装，支持JPA实体实例的生命周期，并允许你用标准的Java Persistence查询语言编写查询。

1、基本JPA配置(EntityManagerFactory--EMF配置)

 

persistence.xml，该文件必须放在被部署的持久化单元的META-INF目录下，由于我这里建的是java project，所以我把META-INF目录放在bin目录下

<persistence xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0"> <persistence-unit name="helloworld"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <!-- <class>hello.Message</class> --> <properties> <property name="hibernate.archive.autodetection" value="class,hbm"/> <property name="hibernate.connection.username" value="root"/> <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/myhibernate"/> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect"/> <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/> <property name="hibernate.hbm2ddl.auto" value="create"/> <property name="hibernate.c3p0.min_size" value="5"/> <property name="hibernate.c3p0.max_size" value="20"/> <property name="hibernate.c3p0.timeout" value="300"/> <property name="hibernate.c3p0.max_statements" value="50"/> <property name="hibernate.c3p0.idle_test_period" value="3000"/> <property name="hibernate.show_sql" value="true"/> <property name="hibernate.connection.password" value=""/> <property name="myeclipse.connection.profile" value="mysql"/> </properties> </persistence-unit> </persistence>

 

实体类Message.java

package hello; import javax.persistence.CascadeType; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.JoinColumn; import javax.persistence.ManyToOne; import javax.persistence.Table; @Entity @Table(name = "Message") public class Message { @Id @GeneratedValue @Column(name = "ID") private Long id; @Column(name = "MESSAGE_TEXT") private String text; @ManyToOne(cascade = CascadeType.ALL) @JoinColumn(name = "NEXT_MESSAGE_ID") private Message nextMessage; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getText() { return text; } public void setText(String text) { this.text = text; } public Message getNextMessage() { return nextMessage; } public void setNextMessage(Message nextMessage) { this.nextMessage = nextMessage; } }

 

测试类HelloWorld.java

package hello; import java.util.Iterator; import java.util.List; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.EntityTransaction; import javax.persistence.Persistence; public class HelloWorld { @SuppressWarnings("unchecked") public static void main(String[] args) { EntityManagerFactory emf = Persistence .createEntityManagerFactory("helloworld"); /*----------1------*/ EntityManager em = emf.createEntityManager(); EntityTransaction tx = em.getTransaction(); tx.begin(); Message message = new Message(); message.setText("hello world"); em.persist(message); tx.commit(); em.close(); /*----------2------*/ EntityManager newEm = emf.createEntityManager(); EntityTransaction newTx = newEm.getTransaction(); newTx.begin(); List messages = newEm.createQuery("select m from Message m order by m.text asc") .getResultList(); System.out.println("messages.size() = " + messages.size()); for (Iterator iter = messages.iterator(); iter.hasNext();) { Message loadedMsg = (Message) iter.next(); System.out.println(loadedMsg.getText()); } newTx.commit(); newEm.close(); emf.close(); } }

 

 

运行结果

messages.size() = 1
hello world

 

说明：

javax.persistence.Persistence   给EntityManagerFactory的创建提供一种静态方法的启动类

javax.persistence.EntityManagerFactory 相当于hibernate的SessionFactory

javax.persistence.EntityManager 相当与hibernate的Session

javax.persistence.Query 相当与hibernate的Query,跟hibernate使用hql一样，同样可以使用对象化的查询语言

javax.persistence.EntityTransaction 相当于hibernate的Transaction