JPA学习1 - 概述、JPA、JPA核心注解、JPA核心对象

JPA

JCP（Java Community Process）Java社区进程组织发布的 Java EE 标准之一，任何声称遵循JPA标准的框架，都提供相同的JPA接口访问。保证JPA开发的企业应用能够经过少量的修改就能够在不同的JPA框架下运行

 
 

JPA-Hibernate集成代码

核心注解

 
 
@GeneratedValue(strategy = GenerationType.TABLE)的介绍

核心对象

简单使用

 
pom.xml

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>


        <!--hibernate对JPA规范的支持包-->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>5.4.30.Final</version>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-all</artifactId>
            <version>5.6.3</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

 
persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="2.0">

    <!-- transaction-type JTA：分布式事务，管理多个数据库的链接 RESOURCE_LOCAL：本地事务，单数据库形式 -->
    <persistence-unit name="myJpa" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <properties>
            <property name="javax.persistence.jdbc.user" value="root"/>
            <property name="javax.persistence.jdbc.password" value="root"/>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/lrc_blog_test?useSSL=false&amp;characterEncoding=UTF-8&amp;serverTimezone=Asia/Shanghai"/>
            <property name="hibernate.show_sql" value="true"/>

            <!-- value: create：@Entity对应的数据库有表，则删除在重新创建新表 update: @Entity对应的数据库有表，则不删除，无表则创建 none：什么都不操作 -->
            <property name="hibernate.hbm2ddl.auto" value="create"/>

        </properties>

    </persistence-unit>
</persistence>

 
Book.java

@Getter
@Setter
@Entity
@Table(name = "book")
@ToString
public class Book implements Serializable {
    
    private static final long serialVersionUID = 2095940921263481761L;



    /** 主键 - 记录插入自动填充主键处理{@path application.yml} */
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id")
    private String id;

    @Column(name = "create_time")
    private String createTime;

    @Column(name = "update_time")
    private String updateTime;

    /** 记录是否被逻辑删除：0未删除 1逻辑删除 - 逻辑处理值定义{@path application.yml}*/
    @Column(name = "is_del")
    private Integer isDel;

    /** 书籍状态；-1违规 0发布且公开 1发布且私密 - 默认0 */
    @Column(name = "status")
    private String status;

    /** 书名 */
    @Column(name = "name")
    private String name;

    /** 作者 */
    @Column(name = "author")
    private String author;

    /** 作者国籍 */
    @Column(name = "country")
    private String country;

    /** 下载地址 */
    @Column(name = "download_url")
    private String downloadUrl;

    /** 文件类型 */
    @Column(name = "file_type")
    private String fileType;

    /** 阅读感受 */
    @Column(name = "reading_feeling")
    private String readingFeeling;

    /** 书籍分享者 - 昵称 */
    @Column(name = "sharer")
    private String sharer;

    /** 书籍是否违规：0未违规 1违规 - 违规不可显示 */
    @Column(name = "is_violation")
    private Integer isViolation;




    //书籍状态
    public final  static String STATUS_VIOLATION = "-1";
    public final  static String STATUS_PUBLISH_PUBLIC = "0";
    public final  static String STATUS_PUBLISH_PRIVATE = "1";

}

 
JpaDemoApplicationTests.java

public class JpaDemoApplicationTests {
    

    EntityManagerFactory entityManagerFactory;
    EntityManager entityManager;
    EntityTransaction transaction;

    @Before
    public void beforeMethod() {
    

        System.out.println("beforeMethod=============");

        entityManagerFactory = Persistence.createEntityManagerFactory("myJpa");
        entityManager = entityManagerFactory.createEntityManager();
        transaction = entityManager.getTransaction();

        //事务开始
        transaction.begin();
    }

    @Test
    public void contextLoads() {
    

        System.out.println("contextLoads=============");

        Book book = entityManager.find(Book.class, "08b756bca4e9644ba05cbf97fe03a5b0");
        System.out.println(book);

        //Article article = new Article();
        //article.setTitle("来广东啦！！");
        //entityManager.persist(article);

    }

    @After
    public void afterMethod() {
    

        System.out.println("afterMethod=============");

        //提交事务
        transaction.commit();
        //释放资源
        entityManager.close();
        entityManagerFactory.close();
    }

}