JavaEE(12) - JPA规范及实现(TopLink和Hibernate)

1. JPA规范与ORM框架之间的联系

JPA规范并不属于EJB3规范，它是一套完全独立的规范，不仅可以在基于EJB的JavaEE应用程序中使用，而且完全可以在普通JavaSE应用程序中使用。

JPA事务管理总结：

运行环境 类型	J2EE环境		J2SE环境
	EJB容器	Web容器
应用托管的 EntityManager	JTA, RESOURCE_LOCAL	JTA, RESOURCE_LOCAL	RESOURCE_LOCAL
容器托管的 EntityManager	JTA	不支持	不支持

常用的3种组件：

1）. 实体：增加了orm.xml映射文件或者Annotation的POJO.

2）. EntityManager：类似于Hibernate框架的Session，使用其对实体进行操作时，JPA规范才可以将这种操作转换为对底层数据库的操作。

3）. JPQL查询：类似于Hibernate提供的HQL查询语言。

#1. TopLink JPA实现(Net Beans创建Java Project, 项目名称：JpaQsTopLink)

实体News.java

package org.crazyit.model;

import javax.persistence.*;

@Entity
@Table(name = "news_table")
public class News {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @Column(name = "NEWS_TITLE", length = 50)
    private String title;

    @Column(nullable = true)
    private String content;

    //构造器
    public News() {
    }

    //标识属性的setter和getter方法
    public void setId(int id) {
        this.id = id;
    }

    public int getId() {
        return (this.id);
    }

    //消息标题的setter方法和getter方法
    public void setTitle(String title) {
        this.title = title;
    }

    public String getTitle() {
        return (this.title);
    }

    //消息内容的setter方法和getter方法
    public void setContent(String content) {
        this.content = content;
    }

    public String getContent() {
        return (this.content);
    }
}

META-INF/persistence.xml(mysql)

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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">
    <persistence-unit name="qs" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <class>org.crazyit.model.News</class>
        <properties>  
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/javaee"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value="******"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLInnoDBDialect"/>           
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
</persistence>

META-INF/persistence.xml(sqlserver)

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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">
    <persistence-unit name="qs" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <class>org.crazyit.model.News</class>
        <properties>  
            <property name="hibernate.connection.driver_class" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
            <property name="hibernate.connection.url" value="jdbc:sqlserver://127.0.0.1:1433;database=javaee"/>
            <property name="hibernate.connection.username" value="javaweb"/>
            <property name="hibernate.connection.password" value="******"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.SQLServerDialect"/>           
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
</persistence>

JpaQs.java

package lee;

import java.util.List;
import javax.persistence.*;

import org.crazyit.model.*;

public class JpaQs {

    //一个持久单元对应一个EntityManagerFactory
    private static final EntityManagerFactory emfactory = Persistence.createEntityManagerFactory("qs");

    public static void main(String[] args) {
        EntityManager em = emfactory.createEntityManager();
        //创建一个News实体
        News news = new News();
        news.setTitle("Crazy Java Union Created!");
        news.setContent("Crazy Java Union Created! Every question will be answered!");
        try {
            System.out.println(news);
            //开启事务
            em.getTransaction().begin();
            //保存实体
            news = em.merge(news);

            System.out.println(news);

            news.setTitle("aaaa");
            //提交事务
            em.getTransaction().commit();
        } 
        finally {
            em.close();
        }
    }
}

#2. Hibernate JPA实现(Net Beans创建Java Project, 项目名称：JpaQsHibernate)

News.java(参见#1)

META-INF/persistence.xml(mysql)

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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">
    <persistence-unit name="qs" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <class>org.crazyit.model.News</class>
        <properties>  
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/javaee"/>
            <property name="hibernate.connection.username" value="root"/>
            <property name="hibernate.connection.password" value="******"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLInnoDBDialect"/>           
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
</persistence>

META-INF/persistence.xml(sqlserver)

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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">
    <persistence-unit name="qs" transaction-type="RESOURCE_LOCAL">
        <provider>oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider</provider>
        <class>org.crazyit.model.News</class>
        <properties>            
            <property name="toplink.jdbc.driver" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>  
            <property name="toplink.jdbc.url" value="jdbc:sqlserver://127.0.0.1:1433;database=javaee"/>
            <property name="toplink.jdbc.user" value="javaweb"/>
            <property name="toplink.jdbc.password" value="******"/>  
            
            <!-- 指定操作的目标数据库类型，可指定为auto，让JPA自动识别
            该属性相当于指定数据库方言，该属性值默认就是Auto(区分大小写) -->
            <property name="toplink.target-database" value="Auto"/>
            <property name="toplink.ddl-generation" value="create-tables"/>
            
            <property name="toplink.jdbc.write-connections.max" value="10"/>
            <property name="toplink.jdbc.write-connections.min" value="5"/>
            <property name="toplink.jdbc.read-connections.max" value="2"/>
            <property name="toplink.jdbc.read-connections.min" value="2"/>
            <property name="toplink.jdbc.read-connections.shared" value="false"/>
        </properties>
    </persistence-unit>
</persistence>

JpaQs.java

package lee;

import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
//import javax.persistence.*;

import org.crazyit.model.*;

public class JpaQs {

    //一个持久单元对应一个EntityManagerFactory
    private static final EntityManagerFactory emfactory = Persistence.createEntityManagerFactory("qs");

    public static void main(String[] args) {
        final EntityManager em = emfactory.createEntityManager();
        News news = new News();
        news.setTitle("Crazy Java Union Created!");
        news.setContent("Crazy Java Union Created! Every question will be answered!");
        try {
            //开启事务
            em.getTransaction().begin();
            //保存实体
            em.persist(news);
            //提交事务
            em.getTransaction().commit();
        } 
        finally {
            em.close();
        }
    }
}

#3. Hibernate XML JPA实现(Net Beans创建Java Project, 项目名称：JpaQsHibernateXml)

News.java

package org.crazyit.model;

import javax.persistence.*;

public class News {

    private int id;
    private String title;
    private String content;

    public News() {
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getId() {
        return (this.id);
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getTitle() {
        return (this.title);
    }

    public void setContent(String content) {
        this.content = content;
    }

    public String getContent() {
        return (this.content);
    }
}

News.orm.xml

<?xml version="1.0" encoding="GBK"?>
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm"
                 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence/orm
    http://java.sun.com/xml/ns/persistence/orm_1_0.xsd" version="1.0">
    <persistence-unit-metadata>
        <persistence-unit-defaults>
            <access>PROPERTY</access>
        </persistence-unit-defaults>
    </persistence-unit-metadata>

    <package>org.crazyit.model</package>
    <entity class="News">

        <table name="news_table"/>
        <attributes>
            <id name="id">
                <generated-value strategy="IDENTITY"/>
            </id>
            <basic name="title">
                <column name="news_title" length="50"/>
            </basic>
            <basic name="content"/>
        </attributes>
    </entity>
</entity-mappings>

persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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">
    <persistence-unit name="qs" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
    　　<mapping-file>org/crazyit/model/News.orm.xml</mapping-file>
        <properties>  
            <property name="hibernate.connection.driver_class" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
            <property name="hibernate.connection.url" value="jdbc:sqlserver://127.0.0.1:1433;database=javaee"/>
            <property name="hibernate.connection.username" value="javaweb"/>
            <property name="hibernate.connection.password" value="P@66word"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.SQLServerDialect"/>           
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
</persistence>

JpaQs.java

package lee;

import java.util.List;
import javax.persistence.*;

import org.crazyit.model.*;

public class JpaQs {
    private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("qs");

    public static void main(String[] args) {
        EntityManager em = emf.createEntityManager();
        try {
            em.getTransaction().begin();
            News news = em.find(News.class, 1);
            news.setContent("疯狂Java联盟的网址：crazyit.org!!");
            em.getTransaction().commit();
        } 
        finally {
            em.close();
        }
    }
}

2. 实体类的要求和状态迁移