JPA的配置文件

一、引入包

 <dependencies>
        <!-- https://mvnrepository.com/artifact/org.hibernate.javax.persistence/hibernate-jpa-2.1-api -->
        <dependency>
            <groupId>org.hibernate.javax.persistence</groupId>
            <artifactId>hibernate-jpa-2.1-api</artifactId>
            <version>1.0.0.Final</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.8-dmr</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.2.17.Final</version>
        </dependency>

    </dependencies>

二、配置resources/META-INF/persistence.xml的书写

<?xml version="1.0" encoding="utf-8" ?>
<!--导入schema约束，此约束来源：复制hibernate-core:5.2.16.Final包下的/org/hibernate/jpa/persistence_2_0.xsd文件中的这一段出来即可。-->
<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">
    <!--配置持久化单元（可以配置多个，名称不能重复）
        name:用于指定持久化单元的名称
        transcation-type:指定事务的类型。
                      JTA:Java Transcation API
                      RESOURCE_LOCAL:指的是本地代码事务
    -->

    <persistence-unit name="myPersistenceUnit" transaction-type="RESOURCE_LOCAL">
        <!--JPA规范提供商，可以不写-->
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <!--指定Jpa注解的实体类型位置，可以不写-->
        <class>com.demo.domain.Customer</class>
        <!--连接相关的一些配置，都是用hibernate的。-->
        <properties>
            <!--第一部分，连接数据库信息-->
            <property name="hibernate.connection.driver_class" value="com.mysql.cj.jdbc.Driver"></property>
            <property name="hibernate.connection.url" value="jdbc:mysql://127.0.0.1:3306/jpademodb?characterEncoding=utf8&amp;useUnicode=true&amp;useSSL=false&amp;serverTimezone=Asia/Shanghai"></property>
            <property name="hibernate.connection.username" value="root"></property>
            <property name="hibernate.connection.password" value="123456"></property>
            <!--说明:数据库的方言，用于存放不同数据库之间的SQL语句差异。-->
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL57Dialect"></property>

            <!--第二部分，hibernate的可选配置-->
            <!--是否显示hiberante的生成的SQL语句-->
            <property name="hibernate.show_sql" value="true"></property>
            <!--是否使用格式化输出SQL语句到控制台-->
            <property name="hibernate.format_sql" value="false"></property>
            <!--采用何种方式生成DDL语句，update表示检测实体类的映射配置与数据库表结构是否一致，不一致，则更新数据库。-->
            <property name="hibernate.hbm2ddl.auto" value="update"></property>
            <!--连接池的配置，这里使用的是c3p0连接池，常用的还有阿里的-->
            <property name="hibernate.connection.provider_class" value="org.hibernate.c3p0.internal.C3P0ConnectionProvider"></property>
        </properties>
    </persistence-unit>
</persistence>

三、实体类写法

package domains;

import org.hibernate.annotations.DynamicUpdate;
import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;

@Entity
@Table(name = "student")
@DynamicUpdate(true)
public class Student {

    @Id
    @GeneratedValue(generator = "uuid2")
    @GenericGenerator(name = "uuid2", strategy = "org.hibernate.id.UUIDGenerator")
    @Column(name = "id",length = 36)
    private String id;
    @Column(name = "name", length = 255)
    private String name;
    @Column(name = "age")
    private Integer age;
    @ManyToOne(targetEntity = Teacher.class)
    @JoinColumn(name = "teacherId", referencedColumnName = "id")
    private Teacher teacher;

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

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

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }
}

package domains;

import org.hibernate.annotations.GenericGenerator;

import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;
import java.util.UUID;

@Entity
@Table(name = "teacher")
public class Teacher {
    @Id
    @GeneratedValue(generator = "uuid2")
    @GenericGenerator(name = "uuid2", strategy = "org.hibernate.id.UUIDGenerator")
    @Column(name = "id",length = 36)
    private String id;
    @Column(name = "name", length = 255)
    private String name;

    @OneToMany(targetEntity = Student.class, mappedBy = "teacher")
    private Set<Student> students = new HashSet<Student>(0);

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<Student> getStudents() {
        return students;
    }

    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}

四、调用处

package business;

import domains.Teacher;

import javax.persistence.*;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        EntityManagerFactory entryManagerFactory = Persistence.createEntityManagerFactory("testdb-persistence-unit");
        EntityManager manager = entryManagerFactory.createEntityManager();
        Query query = manager.createNativeQuery("select * from student");
        List result = query.getResultList();
        System.out.println(result);
        EntityTransaction trans = manager.getTransaction();
        trans.begin();
        Teacher t = new Teacher();
        t.setName("李老师");
        manager.persist(t);
        trans.commit();
        manager.close();
    }
}