【Hibernate】Re04 JPA规范使用

都忘了前面一些小前提，就是数据库需要是存在的，不过写链接参数都会写上的

JPA实现就是和Hibernate类似，也需要对应的配置文件等等。。。

 

1、配置文件必须命名【persistence.xml】且放在classpath目录下的META-INF目录下

<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="jpa.persist" transaction-type="RESOURCE_LOCAL"> <!-- name名称可以自定义。事务类型，本地资源？ -->

        <!-- 配置javax.persistence.spi.PersistenceProvider的实现类 如果只有一个实现，其实也可以不写 -->
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>

        <class>cn.zeal4j.domain.Student</class> <!-- 对应的实体类 -->

        <properties>
            <!-- 链接参数 -->
            <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://IP:Port/jpa?serverTimezone=Asia/Shanghai"/>
            <property name="javax.persistence.jdbc.user" value="root"/>
            <property name="javax.persistence.jdbc.password" value="Password"/>

            <!-- 规范实现者的相关配置 也就是供应商 -->
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="update"/>
        </properties>
    </persistence-unit>
</persistence>

2、编写配置对应的实体类，因为本来就是JPA规范，所以和上一篇的注解使用没有改动

package cn.zeal4j.domain;

/**
 * @author Administrator
 * @file Hibernate
 * @create 2020 09 23 22:09
 */

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;
import java.io.Serializable;
import java.util.Date;

@Entity
@Table(name = "user")
public class User implements Serializable {
    private Integer id;
    private String username;
    private String password;
    private Date reg_time;

    public User() {
    }

    public User(Integer id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public User(Integer id, String username, String password, Date reg_time) {
        this(id, username, password);
        this.reg_time = reg_time;
    }

    @Id // 该注解定义实体标识符的属性
    @GeneratedValue(generator = "increment", strategy = GenerationType.AUTO) // 两个主键生成策略，指示Hibernate如何生成
    @GenericGenerator(name = "increment", strategy = "increment")
    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Temporal(TemporalType.DATE) // 可以对时间类型的数据注解JPA提供的枚举时间类型     DATE,     TIME,     TIMESTAMP;
    @Column(name = "reg_time") // 标注类属性对应的表字段名称
    public Date getReg_time() {
        return reg_time;
    }

    public void setReg_time(Date reg_time) {
        this.reg_time = reg_time;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

3、测试运行：

    @Test
    public void JpaSpecification() {
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("jpa.persist");

        EntityManager entityManager = null;

        EntityTransaction transaction = null;

        try {
            entityManager  = entityManagerFactory.createEntityManager();
            transaction = entityManager.getTransaction();
            transaction.begin();

            entityManager.persist(new Student(null, "学生Zeal4J", 18, 0, new Date(), "12343215531"));

            transaction.commit();

        } catch (Exception exception) {
            exception.printStackTrace();
            transaction.rollback();
        } finally {
            entityManager.close();
        }
    }