5 Hibernate：Java Persistence API (JPA) 入门

Java Persistence API (JPA)，Java 持久层 API，是 JCP 组织发布的 Java EE 标准规范，通过注解或 XML 描述实体对象和数据库表的映射关系。
Hibernate 实现了 JPA 规范，以下展示 Hibernate JPA 开发的完整步骤：

(1) 使用 Maven 管理 Hibernate 依赖

参看 4 Hibernate：使用注解（Annotation）

(2) 创建 JPA 配置文件 `persistence.xml`

Hibernate JPA 开发不需要创建 Hibernate 特定配置文件 hibernate.cfg.xml，取而代之的是创建 JPA 自有配置文件 persistence.xml，JPA 规范定义的启动过程不同于 Hibernate 启动过程。
JPA 配置文件 persistence.xml 需要放在类路径下 META-INF 目录中，内容如下

<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_2_0.xsd"version="2.0"><persistence-unit name="hibernate.jpa"><description>Persistence unit for the JPA tutorial of the Hibernate Getting Started Guide</description><class>hibernate.Person</class><properties><property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" /><property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/test" /><property name="javax.persistence.jdbc.user" value="root" /><property name="javax.persistence.jdbc.password" value="123456" /><property name="hibernate.show_sql" value="true" /><property name="hibernate.hbm2ddl.auto" value="create" /></properties></persistence-unit></persistence>

注意：
需要为 persistence-unit 设置 name 属性，此名称唯一；
对比 hibernate.cfg.xml，除数据库连接配置部分属性名称有所不同，其他配置保持一致。

(3) 使用注解创建持久化类

package hibernate;import java.util.Date;import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;import org.hibernate.annotations.GenericGenerator;@Entity
@Table(name = "person")
public class Person {private int id;private String account;private String name;private Date birth;public Person() {}public Person(String account, String name, Date birth) {this.account = account;this.name = name;this.birth = birth;}@Id // 实体唯一标识@GeneratedValue(generator = "increment") // 使用名为“increment”的生成器@GenericGenerator(name = "increment", strategy = "increment") // 定义名为“increment”的生成器，使用Hibernate的"increment"生成策略，即自增public int getId() {return id;}public void setId(int id) {this.id = id;}public String getAccount() {return account;}public void setAccount(String account) {this.account = account;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Temporal(TemporalType.TIMESTAMP)public Date getBirth() {return birth;}public void setBirth(Date birth) {this.birth = birth;}@Overridepublic String toString() {return "Person [id=" + id + ", account=" + account + ", name=" + name + ", birth=" + birth + "]";}}

(4) 通过 JPA API 编写访问数据库的代码

package hibernate;import java.text.ParseException;
import java.util.Date;
import java.util.List;import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;import org.junit.After;
import org.junit.Before;
import org.junit.Test;public class EntityManagerIllustrationTest {private EntityManagerFactory entityManagerFactory;@Beforepublic void setUp() throws Exception {entityManagerFactory = Persistence.createEntityManagerFactory("hibernate.jpa");}@Afterpublic void tearDown() throws Exception {entityManagerFactory.close();}@Testpublic void test() throws ParseException {EntityManager entityManager = entityManagerFactory.createEntityManager();entityManager.getTransaction().begin();entityManager.persist(new Person("tony", "Tony Stark", new Date()));entityManager.persist(new Person("hulk", "Bruce Banner", new Date()));entityManager.getTransaction().commit();entityManager.close();entityManager = entityManagerFactory.createEntityManager();entityManager.getTransaction().begin();List<Person> result = entityManager.createQuery("FROM Person", Person.class).getResultList();for (Person person : result) {System.out.println(person);}entityManager.getTransaction().commit();entityManager.close();}}

单元测试日志：

六月 26, 2017 12:01:22 上午 org.hibernate.jpa.internal.util.LogHelper logPersistenceUnitInformation
INFO: HHH000204: Processing PersistenceUnitInfo [name: hibernate.jpa...]
六月 26, 2017 12:01:23 上午 org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {5.2.10.Final}
六月 26, 2017 12:01:23 上午 org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
六月 26, 2017 12:01:23 上午 org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.0.1.Final}
六月 26, 2017 12:01:23 上午 org.hibernate.boot.jaxb.internal.stax.LocalXmlResourceResolver resolveEntity
WARN: HHH90000012: Recognized obsolete hibernate namespace http://hibernate.sourceforge.net/hibernate-mapping. Use namespace http://www.hibernate.org/dtd/hibernate-mapping instead.  Support for obsolete DTD/XSD namespaces may be removed at any time.
六月 26, 2017 12:01:28 上午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
六月 26, 2017 12:01:28 上午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [com.mysql.jdbc.Driver] at URL [jdbc:mysql://localhost:3306/test]
六月 26, 2017 12:01:28 上午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {user=root, password=****}
六月 26, 2017 12:01:28 上午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
六月 26, 2017 12:01:28 上午 org.hibernate.engine.jdbc.connections.internal.PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 20 (min=1)
Mon Jun 26 00:01:29 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
六月 26, 2017 12:01:30 上午 org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQL5Dialect
Hibernate: drop table if exists PERSON
六月 26, 2017 12:01:32 上午 org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@73511076] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
Hibernate: create table PERSON (ID integer not null auto_increment, ACCOUNT varchar(255), NAME varchar(255), BIRTH datetime, primary key (ID)) engine=MyISAM
六月 26, 2017 12:01:32 上午 org.hibernate.resource.transaction.backend.jdbc.internal.DdlTransactionIsolatorNonJtaImpl getIsolatedConnection
INFO: HHH10001501: Connection obtained from JdbcConnectionAccess [org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator$ConnectionProviderJdbcConnectionAccess@42257bdd] for (non-JTA) DDL execution was not in auto-commit mode; the Connection 'local transaction' will be committed and the Connection will be set into auto-commit mode.
六月 26, 2017 12:01:33 上午 org.hibernate.tool.schema.internal.SchemaCreatorImpl applyImportSources
INFO: HHH000476: Executing import script 'org.hibernate.tool.schema.internal.exec.ScriptSourceInputNonExistentImpl@4b629f13'
Hibernate: insert into PERSON (ACCOUNT, NAME, BIRTH) values (?, ?, ?)
Hibernate: insert into PERSON (ACCOUNT, NAME, BIRTH) values (?, ?, ?)
六月 26, 2017 12:01:33 上午 org.hibernate.hql.internal.QueryTranslatorFactoryInitiator initiateService
INFO: HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select person0_.ID as ID1_0_, person0_.ACCOUNT as ACCOUNT2_0_, person0_.NAME as NAME3_0_, person0_.BIRTH as BIRTH4_0_ from PERSON person0_
Person [id=1, account=tony, name=Tony Stark, birth=2017-06-26 00:01:33.0]
Person [id=2, account=hulk, name=Bruce Banner, birth=2017-06-26 00:01:34.0]
六月 26, 2017 12:01:34 上午 org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH10001008: Cleaning up connection pool [jdbc:mysql://localhost:3306/test]

数据库查询结果：