JPA 2.HelloWorld
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
