JPA 2.HelloWorld

我不是女神ヾ 2022-05-22 10:18 353阅读 0赞

# JPA HelloWorld #

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## 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 ##

![1][]

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![这里写图片描述][70]

*  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>
            
            <dependency>
                <groupId>org.hibernate</groupId>
                <artifactId>hibernate-core</artifactId>
                <version>5.3.1.Final</version>
            </dependency>
    
            
            <dependency>
                <groupId>org.hibernate</groupId>
                <artifactId>hibernate-entitymanager</artifactId>
                <version>5.3.1.Final</version>
            </dependency>
    
            
            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
                <version>5.1.46</version>
            </dependency>
    
            
            <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">
    	    
            
            
            <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    
            
            <class>jpa.entity.Customer</class>
    
            <properties>
                
                <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"/>
    
                
                <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 ##

![工程结构][70 1]

[1]: /images/20220522/e0d4fc0ed14a435fafad4c5da9f7537d.png
[2]: /images/20220522/10eeb824f94f4506b05da6ab093814ba.png
[70]: /images/20220522/6393e7d6ebb7453e872a2c8ca0776d66.png
[70 1]: /images/20220522/28ce77df040545d993add2df6ccf318a.png