JPA 入门实战(2)--简单使用-百木园

本文主要介绍 JPA 的实际使用，相关的环境及软件信息如下：JPA 2.2(eclipselink 2.7.10、hibernate-entitymanager 5.6.10.Final、openjpa 3.2.2)，JPA 3.0(eclipselink 3.0.2、hibernate-core-jakarta 5.6.10.Final)。

1、JPA 2.2 使用

工程目录结构如下：

1.1、引入依赖

这里使用 eclipselink 作为 JPA 的实现框架。

<dependency>
    <groupId>org.eclipse.persistence</groupId>
    <artifactId>org.eclipse.persistence.jpa</artifactId>
    <version>2.7.10</version>
</dependency>

其他的依赖可自行引入，如数据库驱动、lombok 等。

1.2、创建实体类

1.2.1、Student.java

package com.abc.demojpa.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

import javax.persistence.*;
import java.time.LocalDateTime;

@NoArgsConstructor
@AllArgsConstructor
@Data
@Entity
@Table(name = \"a_student\")
@NamedQuery(name = \"queryAll\", query = \"select s from Student s\")
public class Student {
    @Id
    @GeneratedValue
    private Long id;

    @Column(name = \"create_time\")
    private LocalDateTime createTime;

    @Column(name = \"modify_time\")
    private LocalDateTime modifyTime;

    private String name;

    private Integer age;

    @Column(name = \"home_address\")
    private String homeAddress;
}

1.2.2、BaseEntity.java

package com.abc.demojpa.entity;

import lombok.Data;

import javax.persistence.Column;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.MappedSuperclass;
import java.time.LocalDateTime;

@Data
//该类的属性都将映射到其子类的数据库字段中
@MappedSuperclass
public class BaseEntity {
    @Id
    @GeneratedValue
    private Long id;

    @Column(name = \"create_time\")
    private LocalDateTime createTime;
}

1.2.3、Teacher.java

Teacher 继承了 BaseEntity，主要为了测试属性的继承。

package com.abc.demojpa.entity;

import lombok.Data;
import lombok.NoArgsConstructor;

import javax.persistence.*;

@NoArgsConstructor
@Data
@Entity
@Table(name = \"a_teacher\")
public class Teacher extends BaseEntity {
    private String name;

    private Integer age;
}

1.3、编写 JPA 配置文件 (persistence.xml)

该配置文件需放在 META-INF 目录下。

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<persistence version=\"2.2\"
             xmlns=\"http://xmlns.jcp.org/xml/ns/persistence\"
             xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
             xsi:schemaLocation=\"http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd\">
    <persistence-unit name=\"myUnit\">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <class>com.abc.demojpa.entity.Student</class>
        <class>com.abc.demojpa.entity.Teacher</class>
        <properties>
            <property name=\"javax.persistence.jdbc.driver\" value=\"com.mysql.cj.jdbc.Driver\"/>
            <property name=\"javax.persistence.jdbc.url\" value=\"jdbc:mysql://10.49.196.10:3306/test?useUnicode=true&amp;characterEncoding=UTF-8\"/>
            <property name=\"javax.persistence.jdbc.user\" value=\"root\"/>
            <property name=\"javax.persistence.jdbc.password\" value=\"123456\"/>
            <property name=\"eclipselink.logging.level\" value=\"INFO\" />
            <property name=\"eclipselink.ddl-generation\" value=\"create-or-extend-tables\" />
        </properties>
    </persistence-unit>
</persistence>

eclipselink 开头的配置是 eclipselink 自带的扩展配置，用于实现功能的增强；详细的扩展配置说明可参考官网说明：https://www.eclipse.org/eclipselink/documentation/2.7/jpa/extensions/toc.htm。

1.4、使用例子

1.4.1、插入实体

@Test
public void persist() {
    entityManager.getTransaction().begin();
    Student student = new Student();
    student.setName(\"小明\");
    student.setCreateTime(LocalDateTime.now());
    student.setModifyTime(LocalDateTime.now());
    student.setAge(15);
    student.setHomeAddress(\"江苏\");

    Student student2 = new Student();
    student2.setName(\"小红\");
    student2.setAge(18);
    student2.setHomeAddress(\"广东\");

    Teacher teacher = new Teacher();
    teacher.setCreateTime(LocalDateTime.now());
    teacher.setName(\"张三\");
    teacher.setAge(35);

    entityManager.persist(student);
    entityManager.persist(student2);
    entityManager.persist(teacher);

    entityManager.getTransaction().commit();
}

1.4.2、查询实体

@Test
public void find() {
    Student student = entityManager.find(Student.class, 1501L);
    logger.info(\"student={}\", student);
}

1.4.3、更新实体(先查再更新)

@Test
public void modify() {
    entityManager.getTransaction().begin();
    Student student = entityManager.find(Student.class, 1501L);
    student.setName(\"小明2\");
    entityManager.getTransaction().commit();
}

1.4.4、更新实体(直接根据id更新)

@Test
public void merge() {
    entityManager.getTransaction().begin();
    Student student = new Student();
    student.setId(1501L);
    student.setName(\"小明3\");
    student.setAge(16);
    entityManager.merge(student);
    entityManager.getTransaction().commit();
}

1.4.5、删除实体

@Test
public void remove() {
    entityManager.getTransaction().begin();
    Student student = entityManager.find(Student.class, 1501L);
    entityManager.remove(student);
    entityManager.getTransaction().commit();
}

1.4.6、JPQL 查询

@Test
public void select() {
    //查询一个字段
    Query query = entityManager.createQuery(\"select s.name from Student s where s.age>10\", String.class);
    List<String> result = query.getResultList();
    logger.info(\"result={}\", result);

    //查询多个字段 (?n 占位符：传统 ? 占位符的改良占位符，仅仅适应 JPQL 查询)
    query = entityManager.createQuery(\"select s.name,s.homeAddress from Student s where s.age>?1 and s.name like ?2\", Object[].class);
    query.setParameter(1, 10);
    query.setParameter(2, \"%小%\");
    List<Object[]> result2 = query.getResultList();
    for (Object[] arr : result2) {
        String s = \"\";
        for (Object o : arr) {
            s += o.toString() + \",\";
        }
        logger.info(s);
    }

    //查询对象 (:name 占位符：变量名形式的占位符，仅仅适应 JPQL 查询)
    query = entityManager.createQuery(\"select s.name,s.homeAddress from Student s where s.age between :min and :max and s.name like \'%小%\' order by s.id\", Student.class);
    query.setParameter(\"min\", 10);
    query.setParameter(\"max\", 40);
    //设置结果的开始位置，最大记录条数，可用来实现分页
    query.setFirstResult(0);
    query.setMaxResults(10);
    List<Student> result3 = query.getResultList();
    logger.info(\"result3={}\", result3);

    //聚合操作
    query = entityManager.createQuery(\"select max(s.age) from Student s\");
    Object result4 = query.getSingleResult();
    logger.info(\"result4={}\", result4);

    //对应Student实体类中定义的静态查询”queryAll“
    query = entityManager.createNamedQuery(\"queryAll\");
    List<Student> result5 = query.getResultList();
    logger.info(\"result5={}\", result5);
}

1.4.7、JPQL 更新

@Test
public void update() {
    entityManager.getTransaction().begin();
    Query query = entityManager.createQuery( \"update Student SET age=16 where name=\'小明\'\");
    query.executeUpdate();
    entityManager.getTransaction().commit();
}

1.4.8、JPQL 删除

@Test
public void delete() {
    entityManager.getTransaction().begin();
    Query query = entityManager.createQuery( \"delete from Student where id=1501\");
    query.executeUpdate();
    entityManager.getTransaction().commit();
}

1.4.9、JPQL 本地查询,直接 SQL 语句查询数据

@Test
public void nativeSelect() {
    Query query = entityManager.createNativeQuery(\"select s.* from a_student s where s.age>?\", Student.class);
    query.setParameter(1, 10);
    List<Student> result = query.getResultList();
    logger.info(\"result={}\", result);
}

1.4.10、JPA 标准 API 使用一

类似 SQL：select name from student where name=\'小明\'

@Test
public void criteria() {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<String> criteriaQuery = criteriaBuilder.createQuery(String.class);
    Root<Student> root = criteriaQuery.from(Student.class);
    criteriaQuery.select(root.get(\"name\"));
    criteriaQuery.where(criteriaBuilder.equal(root.get(\"name\"), \"小明\"));
    TypedQuery<String> query = entityManager.createQuery(criteriaQuery);
    List<String> list = query.getResultList();
    logger.info(list.toString());
}

1.4.11、JPA 标准 API 使用二

类似 SQL：select id,name,age from student where age>=10 order by age,name desc

@Test
public void criteria2() {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Student> criteriaQuery = criteriaBuilder.createQuery(Student.class);
    Root<Student> root = criteriaQuery.from(Student.class);
    //Student 实体类需要有对应的构造方法
    criteriaQuery.multiselect(root.get(\"id\"), root.get(\"name\"), root.get(\"age\"), root.get(\"homeAddress\"));
    criteriaQuery.where(criteriaBuilder.ge(root.get(\"age\"), 10));
    criteriaQuery.orderBy(criteriaBuilder.asc(root.get(\"age\"))).orderBy(criteriaBuilder.desc(root.get(\"name\")));
    TypedQuery<Student> query = entityManager.createQuery(criteriaQuery);
    List<Student> list = query.getResultList();
    logger.info(list.toString());
}

1.4.12、JPA 标准 API 使用三

类似 SQL：select age,count(*) from student group by age having age<40

@Test
public void criteria3() {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
    Root<Student> root = criteriaQuery.from(Student.class);
    //Student 实体类需要有对应的构造方法
    criteriaQuery.multiselect(root.get(\"age\"), criteriaBuilder.count(root));
    criteriaQuery.groupBy(root.get(\"age\")).having(criteriaBuilder.lessThan(root.get(\"age\"), 40));
    TypedQuery<Object[]> query = entityManager.createQuery(criteriaQuery);
    List<Object[]> list = query.getResultList();
    for (Object o : list) {
        logger.info(\"o={}\", o);
    }
}

1.5、完整代码

JPA 入门实战(2)--简单使用

package com.abc.demojpa;

import com.abc.demojpa.entity.Student;
import com.abc.demojpa.entity.Teacher;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.persistence.*;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
import java.time.LocalDateTime;
import java.util.List;

public class JpaCase {
    protected static final Logger logger = LoggerFactory.getLogger(JpaCase.class);

    private EntityManagerFactory entityManagerFactory;
    private EntityManager entityManager;

    @Before
    public void before() {
        entityManagerFactory = Persistence.createEntityManagerFactory(\"myUnit\");
        entityManager = entityManagerFactory.createEntityManager();
    }

    @After
    public void after() {
        entityManager.close();
        entityManagerFactory.close();
    }

    //插入实体
    @Test
    public void persist() {
        entityManager.getTransaction().begin();
        Student student = new Student();
        student.setName(\"小明\");
        student.setCreateTime(LocalDateTime.now());
        student.setModifyTime(LocalDateTime.now());
        student.setAge(15);
        student.setHomeAddress(\"江苏\");

        Student student2 = new Student();
        student2.setName(\"小红\");
        student2.setAge(18);
        student2.setHomeAddress(\"广东\");

        Teacher teacher = new Teacher();
        teacher.setCreateTime(LocalDateTime.now());
        teacher.setName(\"张三\");
        teacher.setAge(35);

        entityManager.persist(student);
        entityManager.persist(student2);
        entityManager.persist(teacher);

        entityManager.getTransaction().commit();
    }

    //查询实体
    @Test
    public void find() {
        Student student = entityManager.find(Student.class, 1501L);
        logger.info(\"student={}\", student);
    }

    //更新实体(先查再更新)
    @Test
    public void modify() {
        entityManager.getTransaction().begin();
        Student student = entityManager.find(Student.class, 1501L);
        student.setName(\"小明2\");
        entityManager.getTransaction().commit();
    }

    //更新实体(直接根据id更新)
    @Test
    public void merge() {
        entityManager.getTransaction().begin();
        Student student = new Student();
        student.setId(1501L);
        student.setName(\"小明3\");
        student.setAge(16);
        entityManager.merge(student);
        entityManager.getTransaction().commit();
    }

    //删除实体
    @Test
    public void remove() {
        entityManager.getTransaction().begin();
        Student student = entityManager.find(Student.class, 1501L);
        entityManager.remove(student);
        entityManager.getTransaction().commit();
    }


    //JPQL 查询
    @Test
    public void select() {
        //查询一个字段
        Query query = entityManager.createQuery(\"select s.name from Student s where s.age>10\", String.class);
        List<String> result = query.getResultList();
        logger.info(\"result={}\", result);

        //查询多个字段 (?n 占位符：传统 ? 占位符的改良占位符，仅仅适应 JPQL 查询)
        query = entityManager.createQuery(\"select s.name,s.homeAddress from Student s where s.age>?1 and s.name like ?2\", Object[].class);
        query.setParameter(1, 10);
        query.setParameter(2, \"%小%\");
        List<Object[]> result2 = query.getResultList();
        for (Object[] arr : result2) {
            String s = \"\";
            for (Object o : arr) {
                s += o.toString() + \",\";
            }
            logger.info(s);
        }

        //查询对象 (:name 占位符：变量名形式的占位符，仅仅适应 JPQL 查询)
        query = entityManager.createQuery(\"select s.name,s.homeAddress from Student s where s.age between :min and :max and s.name like \'%小%\' order by s.id\", Student.class);
        query.setParameter(\"min\", 10);
        query.setParameter(\"max\", 40);
        //设置结果的开始位置，最大记录条数，可用来实现分页
        query.setFirstResult(0);
        query.setMaxResults(10);
        List<Student> result3 = query.getResultList();
        logger.info(\"result3={}\", result3);

        //聚合操作
        query = entityManager.createQuery(\"select max(s.age) from Student s\");
        Object result4 = query.getSingleResult();
        logger.info(\"result4={}\", result4);

        //对应Student实体类中定义的静态查询”queryAll“
        query = entityManager.createNamedQuery(\"queryAll\");
        List<Student> result5 = query.getResultList();
        logger.info(\"result5={}\", result5);
    }

    //JPQL 更新
    @Test
    public void update() {
        entityManager.getTransaction().begin();
        Query query = entityManager.createQuery( \"update Student SET age=16 where name=\'小明\'\");
        query.executeUpdate();
        entityManager.getTransaction().commit();
    }

    //JPQL 删除
    @Test
    public void delete() {
        entityManager.getTransaction().begin();
        Query query = entityManager.createQuery( \"delete from Student where id=1501\");
        query.executeUpdate();
        entityManager.getTransaction().commit();
    }

    //本地查询,直接 SQL 语句查询数据
    @Test
    public void nativeSelect() {
        Query query = entityManager.createNativeQuery(\"select s.* from a_student s where s.age>?\", Student.class);
        query.setParameter(1, 10);
        List<Student> result = query.getResultList();
        logger.info(\"result={}\", result);
    }

    /**
     * Criteria API
     * select name from student where name=\'小明\'
     */
    @Test
    public void criteria() {
        CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
        CriteriaQuery<String> criteriaQuery = criteriaBuilder.createQuery(String.class);
        Root<Student> root = criteriaQuery.from(Student.class);
        criteriaQuery.select(root.get(\"name\"));
        criteriaQuery.where(criteriaBuilder.equal(root.get(\"name\"), \"小明\"));
        TypedQuery<String> query = entityManager.createQuery(criteriaQuery);
        List<String> list = query.getResultList();
        logger.info(list.toString());
    }

    /**
     * Criteria API
     * select id,name,age from student where age>=10 order by age,name desc
     */
    @Test
    public void criteria2() {
        CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
        CriteriaQuery<Student> criteriaQuery = criteriaBuilder.createQuery(Student.class);
        Root<Student> root = criteriaQuery.from(Student.class);
        //Student 实体类需要有对应的构造方法
        criteriaQuery.multiselect(root.get(\"id\"), root.get(\"name\"), root.get(\"age\"), root.get(\"homeAddress\"));
        criteriaQuery.where(criteriaBuilder.ge(root.get(\"age\"), 10));
        criteriaQuery.orderBy(criteriaBuilder.asc(root.get(\"age\"))).orderBy(criteriaBuilder.desc(root.get(\"name\")));
        TypedQuery<Student> query = entityManager.createQuery(criteriaQuery);
        List<Student> list = query.getResultList();
        logger.info(list.toString());
    }

    /**
     * Criteria API
     * select age,count(*) from student group by age having age<40
     */
    @Test
    public void criteria3() {
        CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
        CriteriaQuery<Object[]> criteriaQuery = criteriaBuilder.createQuery(Object[].class);
        Root<Student> root = criteriaQuery.from(Student.class);
        //Student 实体类需要有对应的构造方法
        criteriaQuery.multiselect(root.get(\"age\"), criteriaBuilder.count(root));
        criteriaQuery.groupBy(root.get(\"age\")).having(criteriaBuilder.lessThan(root.get(\"age\"), 40));
        TypedQuery<Object[]> query = entityManager.createQuery(criteriaQuery);
        List<Object[]> list = query.getResultList();
        for (Object o : list) {
            logger.info(\"o={}\", o);
        }
    }
}

JpaCase.java

2、使用 hibernate 作为 JPA 实现框架

只需修改引入的依赖及 JPA 配置文件(persistence.xml)。

2.1、引入依赖

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-entitymanager</artifactId>
    <version>5.6.10.Final</version>
</dependency>

2.2、增强注解

hibernate 提供一些增强注解使得 JPA 的使用更加方便。@CreationTimestamp 用于自动生成插入时间，@UpdateTimestamp 用于自动生成修改时间。修改实体类如下：

package com.abc.demojpa.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.hibernate.annotations.CreationTimestamp;
import org.hibernate.annotations.UpdateTimestamp;

import javax.persistence.*;
import java.time.LocalDateTime;

@NoArgsConstructor
@AllArgsConstructor
@Data
@Entity
@Table(name = \"a_student\")
@NamedQuery(name = \"queryAll\", query = \"select s from Student s\")
public class Student {
    @Id
    @GeneratedValue
    private Long id;

    @CreationTimestamp
    @Column(name = \"create_time\")
    private LocalDateTime createTime;

    @UpdateTimestamp
    @Column(name = \"modify_time\")
    private LocalDateTime modifyTime;

    private String name;

    private Integer age;

    @Column(name = \"home_address\")
    private String homeAddress;
}

这样就可以不用手动设置 createTime,modifyTime 了。

2.3、persistence.xml

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<persistence version=\"2.2\"
             xmlns=\"http://xmlns.jcp.org/xml/ns/persistence\"
             xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
             xsi:schemaLocation=\"http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd\">
    <persistence-unit name=\"myUnit\">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name=\"javax.persistence.jdbc.driver\" value=\"com.mysql.cj.jdbc.Driver\"/>
            <property name=\"javax.persistence.jdbc.url\" value=\"jdbc:mysql://10.49.196.10:3306/test?useUnicode=true&amp;characterEncoding=UTF-8\"/>
            <property name=\"javax.persistence.jdbc.user\" value=\"root\"/>
            <property name=\"javax.persistence.jdbc.password\" value=\"123456\"/>
            <property name=\"hibernate.hbm2ddl.auto\" value=\"update\"/>
        </properties>
    </persistence-unit>
</persistence>

hibernatee 开头的配置是 hibernate 自带的扩展配置，用于实现功能的增强；详细的配置说明可参考官网说明：https://docs.jboss.org/hibernate/orm/5.6/userguide/html_single/Hibernate_User_Guide.html#configurations。

3、使用 OpenJPA 作为 JPA 实现框架

只需修改引入的依赖及 JPA 配置文件(persistence.xml)。

2.1、引入依赖

<dependency>
    <groupId>org.apache.openjpa</groupId>
    <artifactId>openjpa-all</artifactId>
    <version>3.2.2</version>
</dependency>

2.2、persistence.xml

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<persistence version=\"2.2\"
             xmlns=\"http://xmlns.jcp.org/xml/ns/persistence\"
             xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
             xsi:schemaLocation=\"http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd\">
    <persistence-unit name=\"myUnit\">
        <provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>
        <class>com.abc.demojpa.entity.Student</class>
        <class>com.abc.demojpa.entity.BaseEntity</class>
        <class>com.abc.demojpa.entity.Teacher</class>
        <properties>
            <property name=\"javax.persistence.jdbc.driver\" value=\"com.mysql.cj.jdbc.Driver\"/>
            <property name=\"javax.persistence.jdbc.url\" value=\"jdbc:mysql://10.49.196.10:3306/cqt?useUnicode=true&amp;characterEncoding=UTF-8\"/>
            <property name=\"javax.persistence.jdbc.user\" value=\"root\"/>
            <property name=\"javax.persistence.jdbc.password\" value=\"123456\"/>
            <property name=\"openjpa.jdbc.SynchronizeMappings\" value=\"buildSchema(ForeignKeys=true)\"/>
            <property name=\"openjpa.ClassLoadEnhancement\" value=\"true\" />
            <property name=\"openjpa.DynamicEnhancementAgent\" value=\"true\" />
            <property name=\"openjpa.RuntimeUnenhancedClasses\" value=\"supported\" />
        </properties>
    </persistence-unit>
</persistence>

openjpa 开头的配置是 openjpa 自带的扩展配置，用于实现功能的增强；详细的配置说明可参考官网说明：https://openjpa.apache.org/builds/3.2.2/apache-openjpa/docs/manual.html#ref_guide_conf。

4、JPA 3.0 使用

JavaEE 8 之后，Oracle 已将其捐献给 Eclipse 基金会运作，名字也改为 Jakarta EE。JPA 3.0 作为 Jakarta EE 9 的一部分，主要变化是包名的变化及 xml 配置文件命名空间的变化，功能上与 JPA 2.2 基本一致。

4.1、Eclipselink 作为实现框架

4.1.1、引入依赖

<dependency>
    <groupId>jakarta.persistence</groupId>
    <artifactId>jakarta.persistence-api</artifactId>
    <version>3.0.0</version>
</dependency>
<dependency>
    <groupId>org.eclipse.persistence</groupId>
    <artifactId>org.eclipse.persistence.jpa</artifactId>
    <version>3.0.2</version>
</dependency>

4.1.2、persistence.xml

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<persistence xmlns=\"https://jakarta.ee/xml/ns/persistence\"
             xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
             version=\"3.0\"
             xsi:schemaLocation=\"https://jakarta.ee/xml/ns/persistence https://jakarta.ee/xml/ns/persistence/persistence_3_0.xsd\">
    <persistence-unit name=\"myUnit\">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <class>com.abc.demojpa.entity.Student</class>
        <class>com.abc.demojpa.entity.Teacher</class>
        <properties>
            <property name=\"jakarta.persistence.jdbc.driver\" value=\"com.mysql.cj.jdbc.Driver\"/>
            <property name=\"jakarta.persistence.jdbc.url\" value=\"jdbc:mysql://10.49.1196.10:3306/cqt?useUnicode=true&amp;characterEncoding=UTF-8\"/>
            <property name=\"jakarta.persistence.jdbc.user\" value=\"root\"/>
            <property name=\"jakarta.persistence.jdbc.password\" value=\"123456\"/>
            <property name=\"eclipselink.logging.level\" value=\"INFO\" />
            <property name=\"eclipselink.ddl-generation\" value=\"create-or-extend-tables\" />
        </properties>
    </persistence-unit>
</persistence>

4.1.3、创建实体类

package com.abc.demojpa.entity;

import jakarta.persistence.*;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;


@NoArgsConstructor
@AllArgsConstructor
@Data
@Entity
@Table(name = \"a_student\")
@NamedQuery(name = \"queryAll\", query = \"select s from Student s\")
public class Student {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    private Integer age;

    @Column(name = \"home_address\")
    private String homeAddress;
}

4.1.4、使用

package com.abc.deomjpa;

import com.abc.demojpa.entity.Student;
import jakarta.persistence.*;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


public class JpaCase {
    protected static final Logger logger = LoggerFactory.getLogger(JpaCase.class);

    private EntityManagerFactory entityManagerFactory;
    private EntityManager entityManager;

    @Before
    public void before() {
        entityManagerFactory = Persistence.createEntityManagerFactory(\"myUnit\");
        entityManager = entityManagerFactory.createEntityManager();
    }

    @After
    public void after() {
        entityManager.close();
        entityManagerFactory.close();
    }

    //查询实体
    @Test
    public void find() {
        Student student = entityManager.find(Student.class, 1501L);
        logger.info(\"student={}\", student);
    }
}

4.2、Hibernate 作为实现框架

主要修改依赖及 JPA 配置文件即可。

4.2.1、引入依赖

<dependency>
    <groupId>jakarta.persistence</groupId>
    <artifactId>jakarta.persistence-api</artifactId>
    <version>3.0.0</version>
</dependency>

<dependency>
    <groupId>jakarta.transaction</groupId>
    <artifactId>jakarta.transaction-api</artifactId>
    <version>2.0.1</version>
</dependency>
<dependency>
    <groupId>jakarta.xml.bind</groupId>
    <artifactId>jakarta.xml.bind-api</artifactId>
    <version>3.0.1</version>
</dependency>
<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-core-jakarta</artifactId>
    <version>5.6.10.Final</version>
</dependency>

4.2.2、persistence.xml

<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<persistence xmlns=\"https://jakarta.ee/xml/ns/persistence\"
             xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\"
             version=\"3.0\"
             xsi:schemaLocation=\"https://jakarta.ee/xml/ns/persistence https://jakarta.ee/xml/ns/persistence/persistence_3_0.xsd\">
    <persistence-unit name=\"myUnit\">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name=\"jakarta.persistence.jdbc.driver\" value=\"com.mysql.cj.jdbc.Driver\"/>
            <property name=\"jakarta.persistence.jdbc.url\" value=\"jdbc:mysql://10.49.196.10:3306/cqt?useUnicode=true&amp;characterEncoding=UTF-8\"/>
            <property name=\"jakarta.persistence.jdbc.user\" value=\"root\"/>
            <property name=\"jakarta.persistence.jdbc.password\" value=\"123456\"/>
            <property name=\"hibernate.show_sql\" value=\"true\"/>
            <property name=\"hibernate.hbm2ddl.auto\" value=\"update\"/>
        </properties>
    </persistence-unit>
</persistence>

如何从 JPA 2.1 迁移到 JPA 3.0 可参考这篇文章：https://thorben-janssen.com/migrating-jpa-2-x-to-3-0。

JPA 2.1 和 JPA 3.0 配置文件差异说明可参考这篇文章：https://thorben-janssen.com/jpa-persistence-xml。

来源：https://www.cnblogs.com/wuyongyin/p/16516717.html
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JPA 入门实战(2)--简单使用

1、JPA 2.2 使用

1.1、引入依赖

1.2、创建实体类

1.2.1、Student.java

1.2.2、BaseEntity.java

1.2.3、Teacher.java

1.3、编写 JPA 配置文件 (persistence.xml)

1.4、使用例子

1.4.1、插入实体

1.4.2、查询实体

1.4.3、更新实体(先查再更新)

1.4.4、更新实体(直接根据id更新)

1.4.5、删除实体

1.4.6、JPQL 查询

1.4.7、JPQL 更新

1.4.8、JPQL 删除

1.4.9、JPQL 本地查询,直接 SQL 语句查询数据

1.4.10、JPA 标准 API 使用一

1.4.11、JPA 标准 API 使用二

1.4.12、JPA 标准 API 使用三

1.5、完整代码

2、使用 hibernate 作为 JPA 实现框架

2.1、引入依赖

2.2、增强注解

2.3、persistence.xml

3、使用 OpenJPA 作为 JPA 实现框架

2.1、引入依赖

2.2、persistence.xml

4、JPA 3.0 使用

4.1、Eclipselink 作为实现框架

4.1.1、引入依赖

4.1.2、persistence.xml

4.1.3、创建实体类

4.1.4、使用

4.2、Hibernate 作为实现框架

4.2.1、引入依赖

4.2.2、persistence.xml

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