一.初识JPA2.0

JPA概述
JPA是独立于SQL ，基于JDBC之上的抽象层。所有类和注解都在javax.persistence包中。

JPA主要组件：
1.ORM，对象和数据库数据之间的映射
2.An entity manager API执行数据库相关操作，CRUD(Create, Read, Update, Delete)
3.JPQL(The Java Persistence Query Language) 用面向对象的查询语言查询数据
4.事务和锁机制
5.回调(Callbacks)和监听器(listeners)定制持久化生命周期逻辑

JPA2.0新特征：
1.基本数据类型(String, Integer, etc.)的集合和嵌入对象的集合可以映射到不同的表中。之前，你仅能映射实体的集合。
2.Map支持被扩展(Map映射)，maps的keys和values可以是基本类型，实体，嵌入对象。
3.加入@OrderColumn注解维护持久化排序。
4.关系映射中父对象被移除，子对象被移除(Orphan removal的支持)。
5.悲观锁的支持。
6.引进新的Criteria API，基于面向对象方式的查询。
7.JPQL语法支持case expressions。
8.嵌入对象可以嵌入其他嵌入对象，并与之关系映射。
9.dot(.)导航语法被扩展，处理关系映射中嵌入对象，嵌入对象的嵌入对象。
10.新的缓存API被加入。
11.persistence.xml文件中一些属性被标准化，增加程序的可移植性。

我们先看一个简单的例子。

我的运行环境是 eclipse+mvn

1. 在 maven 插件中添加附件archetype-catalog.zip中的 local Archetype

 

2. 创建 maven project ， Filter ： weld ，选择 Artifact Id ： jboss-javaee6-webapp, 该 archetype 可以快速创建 JavaEE6 项目，更多信息： http://seamframework.org/Documentation/CDIQuickstartForMavenUsers

 

 

3 . 填写 maven 坐标

 

 

4. 我们现在删除一些我们现在不需要的代码，删除org.example.myproject.controller，org.example.myproject.data，org.example.myproject.rest包，删除org.example.myproject.model.Member类，org.example.myproject.test.MemberRegistrationTest测试类。

5. 好了，现在我们需要创建我们自己的实体类

package org.example.myproject.model;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.NamedQuery;

@Entity
@NamedQuery(name="findAllBooks",query="select b from Book b")
public class Book {
	@Id @GeneratedValue
	private Long id;
	@Column(nullable=false)
	private String title;
	private Float price;
	@Column(length=2000)
	private String description;
	private String isbn;
	private Integer nbOfPage;
	private Boolean illustrations;
	
	public Long getId() {
		return id;
	}
	public void setId(Long id) {
		this.id = id;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public Float getPrice() {
		return price;
	}
	public void setPrice(Float price) {
		this.price = price;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	public String getIsbn() {
		return isbn;
	}
	public void setIsbn(String isbn) {
		this.isbn = isbn;
	}
	public Integer getNbOfPage() {
		return nbOfPage;
	}
	public void setNbOfPage(Integer nbOfPage) {
		this.nbOfPage = nbOfPage;
	}
	public Boolean getIllustrations() {
		return illustrations;
	}
	public void setIllustrations(Boolean illustrations) {
		this.illustrations = illustrations;
	}
	
}

 

还有我们的测试代码：

package org.example.myproject.test;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNotNull;

import java.sql.SQLException;
import java.util.List;

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

import org.example.myproject.model.Book;
import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;

public class BookTest {
	private static EntityManagerFactory emf;
	private static EntityManager em;
	private static EntityTransaction tx;

	@BeforeClass
	public static void initEntityManager() throws Exception {
		emf = Persistence.createEntityManagerFactory("primary");
		em = emf.createEntityManager();
	}

	@AfterClass
	public static void closeEntityManager() throws SQLException {
		em.close();
		emf.close();
	}

	@Before
	public void initTransaction() {
		tx = em.getTransaction();
	}

	@Test
	public void shouldCreateABook() throws Exception {
		// Creates an instance of book
		assertNotNull("EMF should not be null", emf);
		Book book = new Book();
		book.setTitle("The Hitchhiker's Guide to the Galaxy");
		book.setPrice(12.5F);
		book.setDescription("Science fiction comedy book");
		book.setIsbn("1-84023-742-2");
		book.setNbOfPage(354);
		book.setIllustrations(false);
		// Persists the book to the database
		tx.begin();
		em.persist(book);
		tx.commit();
		assertNotNull("ID should not be null", book.getId());
		// Retrieves all the books from the database
		List<Book> books = em.createNamedQuery("findAllBooks").getResultList();
		assertEquals(1, books.size());
	}
}

6. 我们现在要修改 persistence.xml 文件

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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_2_0.xsd">
    <persistence-unit name="primary">
        <!-- You can force a non-default JPA provider using one of these declarations -->
        <!--
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider> -->
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <class>org.example.myproject.model.Book</class>

        <!-- jdbc/__default is the default data source in GlassFish -->
        <!-- A matching data source is added to JBoss AS by deploying the project file default-ds.xml 
        <jta-data-source>jdbc/__default</jta-data-source>-->
        <properties>
            <!-- Properties for Hibernate (default provider for JBoss AS) -->
            <property name="hibernate.hbm2ddl.auto" value="create" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.format_sql" value="false" />

            <!-- Properties for EclipseLink (default provider for GlassFish) -->
            <property name="eclipselink.ddl-generation" value="drop-and-create-tables" />
            <property name="eclipselink.logging.level" value="FINE" />
            
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
			<property name="javax.persistence.jdbc.url"
				value="jdbc:mysql://localhost:3306/javaee6" />
			<property name="javax.persistence.jdbc.user" value="root" />
			<property name="javax.persistence.jdbc.password" value="" />
        </properties>
    </persistence-unit>
</persistence>

 

把 src/main/resources 下的 META-INF 目录 ( 包含 persistence.xml) 复制到 src/test/resources

目录下

记得要创建数据库 javaee6 ，改写你自己的用户名密码

7. 下一步就是要修改 pom.xml 了，添加依赖包坐标

		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-commons-annotations</artifactId>
			<version>3.2.0.Final</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-core</artifactId>
			<version>3.6.0.Final</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-entitymanager</artifactId>
			<version>3.6.0.Final</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>slf4j-log4j12</artifactId>
			<version>1.5.6</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>mysql</groupId>
			<artifactId>mysql-connector-java</artifactId>
			<version>5.1.16</version>
			<scope>test</scope>
		</dependency>

 并修改profile id为default的跳过测试配置值为false

					<plugin>
						<artifactId>maven-surefire-plugin</artifactId>
						<version>2.4.3</version>
						<configuration>
							<skip>false</skip>
						</configuration>
					</plugin>

8. 运行 maven test 。就可以看到数据库中已经多了一张 book 表，并插入了值。