5 Hibernate：Java Persistence API (JPA) 入門

Java Persistence API (JPA)，Java 持久層 API，是 JCP 組織發佈的 java EE 標準規範，經過註解或 XML 描述實體對象和數據庫表的映射關係。

Hibernate 實現了 JPA 規範，如下展現 Hibernate JPA 開發的完整步驟：

1 使用 Maven 管理 Hibernate 依賴

參看 4 Hibernate：使用註解（Annotation）

2 建立 JPA 配置文件 persistence.xml

Hibernate JPA 開發不須要建立 Hibernate 特定配置文件 hibernate.cfg.xml，取而代之的是建立 JPA 自有配置文件 persistence.xml，JPA 規範定義的啓動過程不一樣於 Hibernate 啓動過程。

<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：

• 須要爲 persistence-unit 設置 name 屬性，此名稱惟一；
• 對比 hibernate.cfg.xml，除數據庫鏈接配置部分屬性名稱有所不一樣，其餘配置保持一致。

3 使用註解建立持久化類

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 // 實體惟一標識
    @GeneratedValue(generator = "increment") // 使用名爲「increment」的生成器
    @GenericGenerator(name = "increment", strategy = "increment") // 定義名爲「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;
    }

    @Override
    public String toString() {
        return "Person [id=" + id + ", account=" + account + ", name=" + name + ", birth=" + birth + "]";
    }

}

4 經過 JPA API 編寫訪問數據庫的代碼

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;

    @Before
    public void setUp() throws Exception {
        entityManagerFactory = Persistence.createEntityManagerFactory("hibernate.jpa");
    }

    @After
    public void tearDown() throws Exception {
        entityManagerFactory.close();
    }

    @Test
    public 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();
    }

}

單元測試日誌：

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]

數據庫查詢結果：