Hibernate实战_笔记10

使用Hibernate EntityManager

1、基本的JPA配置

      SessionFactory在Hibernate应用程序中表示一个特定的逻辑数据存储配置。EntityManagerFactory在JPA应用程序中扮演着同样的角色，你用配置文件或者在应用程序代码中配置EntityManagerFactory(EMF)，就像配置SessionFactory一样。EMF的配置，与一组映射元数据（通常是被注解的类）一起，被称作持久化单元（persistence unit）。

<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">
    	<properties>
    		<property name="hibernate.ejb.cfgfile" value="/hibernate.cfg.xml" />
    	</properties>
    </persistence-unit>
</persistence>

<property name="src.etc.dir" value="etc" />
	<!--复制xml、properties后缀文件到bin目录-->
	<target name="copymetafiles">
		<copy todir="${build.dir}">
			<fileset dir="${src.java.dir}">
				<patternset refid="meta.files" />
			</fileset>
		</copy>
		<copy todir="${build.dir}">
			<fileset dir="${src.etc.dir}">
				<patternset refid="meta.files" />
			</fileset>
		</copy>
	</target>

2、使用JPA的“Hello World”

package cn.jbit.jta.util;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public final class JPAUtil {

	private static final EntityManagerFactory emf;
	
	static {
		try{
		emf = Persistence.createEntityManagerFactory("helloworld");
		}catch(Throwable ex){
			throw new ExceptionInInitializerError(ex);
		}
	}
	
	private JPAUtil(){
	}

	public static EntityManagerFactory getEmf() {
		return emf;
	}
	
	public static EntityManager getEntityManager(){
		return emf.createEntityManager();
	}
	
	public static void shutdown(){
		emf.close();
	}
}

package cn.jbit.jta.test;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;

import cn.jbit.jta.entity.Message;
import cn.jbit.jta.util.JPAUtil;

public class EntityManagerTest {
	
	@SuppressWarnings("unchecked")
	public static void main(String[] args) {
		// 第一个单元
		// createEntityMangaerFacoty参数"helloworld"是persistence.xml文件中持久化单元名称
		EntityManager em = JPAUtil.getEntityManager();
		EntityTransaction tx = em.getTransaction();
		tx.begin();

		Message message = new Message("Hello World");
		em.persist(message);

		tx.commit();
		em.close();

		// 第二个单元
		EntityManager secondEm = JPAUtil.getEntityManager();
		EntityTransaction secondTx = secondEm.getTransaction();
		secondTx.begin();
		
		List<Message> messages = secondEm.createQuery(
				"select m from Message m order by m.text asc").getResultList();
		System.out.println(messages.size() + "条消息记录");
		for (Message m : messages) {
			System.out.println(m.getText());
		}
		secondTx.commit();
		secondEm.close();
		
		JPAUtil.shutdown();
	}
}

3、元数据的自动侦测

<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>cn.jbit.jta.entity.Message</class> -->
    	<properties>
    		<!-- 
    		<property name="hibernate.ejb.cfgfile" value="/hibernate.cfg.xml" /> -->
    		<property name="hibernate.archive.autodetection" value="class,hbm"/>
    		<property name="hibernate.show_sql" value="true"/>
    		<property name="hibernate.format_sql" value="true"/>
    		<property name="hibernate.connection.driver_class" value="oracle.jdbc.driver.OracleDriver"/>
    		<property name="hibernate.connection.url" value="jdbc:oracle:thin:@localhost:1521:orcl"/>
    		<property name="hibernate.connection.username" value="system"/>
    		<property name="hibernate.connection.password" value="bdqn"/>
    		<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.dialect" value="org.hibernate.dialect.OracleDialect"/>
    		<property name="hibernate.hbm2ddl.auto" value="create"/>
    	</properties>
    </persistence-unit>
</persistence>

代码提供下载

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Hibernate实战_笔记10

原文：http://blog.csdn.net/com185272358/article/details/20774527