JPA

@Author:hanguixian

@Email:hn_hanguixian@163.com

二 JPA HelloWorld

使用JPA持久化对象的步骤

1.创建 persistence.xml, 在这个文件中配置持久化单元

• 需要指定跟哪个数据库进行交互;

• 需要指定 JPA 使用哪个持久化的框架以及配置该框架的基本属性

2.创建实体类, 使用 annotation 来描述实体类跟数据库表之间的映射关系.

3.使用 JPA API 完成数据增加、删除、修改和查询操作

• 创建 EntityManagerFactory (对应 Hibernate 中的 SessionFactory)

• 创建 EntityManager (对应 Hibernate 中的Session)

在IntelliJ IDEA 下，创建JPA的Maven工程

• pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ifox.hgx</groupId>
    <artifactId>jpa_m2</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.3.1.Final</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-entitymanager -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>5.3.1.Final</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

persistence.xml

• JPA 规范要求在类路径的 META-INF 目录下放置persistence.xml，文件的名称是固定的

• persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence" version="2.1"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_1.xsd">


    <persistence-unit name="jpa_m2" transaction-type="RESOURCE_LOCAL">
        <!--配置使用什么 ORM 产品来作为 JPA 的实现 -->
        <!--5.2版本以后，无法使用HibernatePersistence-->
        <!--如果JPA项目中只有一个实现产品，可以配置不这个节点-->
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

        <!--添加持久化类-->
        <class>jpa.entity.Customer</class>

        <properties>
            <!-- 连接数据库的基本信息 -->
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql:///jpa"/>
            <property name="javax.persistence.jdbc.user" value="root"/>
            <property name="javax.persistence.jdbc.password" value="123456"/>

            <!-- 配置 JPA 实现产品的基本属性. 配置 hibernate 的基本属性 -->
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>

        </properties>
    </persistence-unit>

</persistence>

实体类:Customer

package jpa.entity;

import javax.persistence.*;

@Table(name = "JPA_CUSTOMTERS")
@Entity
public class Customer {


    private Integer id ;
    private String lastName ;

    private String email ;
    private Integer age ;

//    GeneratedValue 生成方式:策略为 GenerationType.AUTO 自动选择
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Id
    public Integer getId() {
        return id;
    }

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

    @Column(name = "LAST_NAME")
    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }





}

测试:

package jpa;

import jpa.entity.Customer;

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

public class TestHello {
    public static void main(String[] args) {

        //1. 创建 EntityManagerFactory
        //注意此处需要和persistence.xml下的persistence-unit name值相同
        String persistenceUnitName = "jpa_m2";
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(persistenceUnitName);


        //2. 创建 EntityManager. 类似于 Hibernate 的 SessionFactory
        EntityManager entityManager = entityManagerFactory.createEntityManager();

        //3. 开启事务
        EntityTransaction transaction = entityManager.getTransaction();
        transaction.begin();

        //4. 进行持久化操作
        Customer customer = new Customer();
        customer.setAge(12);
        customer.setEmail("tom@153.com");
        customer.setLastName("Tom");

        entityManager.persist(customer);

        //5. 提交事务
        transaction.commit();

        //6. 关闭 EntityManager
        entityManager.close();

        //7. 关闭 EntityManagerFactory
        entityManagerFactory.close();
    }
}

工程结构