JPA简介
JPA是什么
JPA 是Java Persistence API的缩写,是一套由Java官方制定的ORM标准。当制定这套标准以后,市场上就出现很多JPA框架。如:OpenJPA(apache),EclipseTop(linktop)(eclipse),Hibernate。
1、如何使用
引入依赖
<properties>
<maven.compiler.source>17maven.compiler.source>
<maven.compiler.target>17maven.compiler.target>
<project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
<lombok.version>1.18.24lombok.version>
<slf4j.version>1.7.25slf4j.version>
<spring.version>5.3.21spring.version>
<junit.version>5.8.2junit.version>
<mysql.version>8.0.30mysql.version>
<HikariCP.version>5.0.1HikariCP.version>
<jpa.version>3.1.0jpa.version>
<hibernateORM.version>6.1.0.FinalhibernateORM.version>
<hibernate.version>5.6.9.Finalhibernate.version>
properties>
<dependencies>
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<version>${lombok.version}version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-apiartifactId>
<version>${slf4j.version}version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-log4j12artifactId>
<version>${slf4j.version}version>
dependency>
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-contextartifactId>
<version>${spring.version}version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>${mysql.version}version>
dependency>
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-testartifactId>
<version>${spring.version}version>
dependency>
<dependency>
<groupId>org.junit.jupitergroupId>
<artifactId>junit-jupiter-apiartifactId>
<version>${junit.version}version>
dependency>
<dependency>
<groupId>com.zaxxergroupId>
<artifactId>HikariCPartifactId>
<version>5.0.1version>
dependency>
<dependency>
<groupId>jakarta.persistencegroupId>
<artifactId>jakarta.persistence-apiartifactId>
<version>${jpa.version}version>
dependency>
<dependency>
<groupId>org.hibernategroupId>
<artifactId>hibernate-coreartifactId>
<version>${hibernateORM.version}version>
dependency>
<dependency>
<groupId>org.hibernate.ormgroupId>
<artifactId>hibernate-hikaricpartifactId>
<version>${hibernateORM.version}version>
dependency>
<dependency>
<groupId>org.hibernategroupId>
<artifactId>hibernate-core-jakartaartifactId>
<version>${hibernate.version}version>
dependency>
dependencies>
数据库脚本
use yootk;
create table course
(
cid bigint auto_increment comment '课程id',
cname varchar(50) comment '课程名称',
start date comment '课程开始时间',
end date comment '课程结束时间',
credit int comment '课程学分',
num int comment '课程人数',
constraint pk_cid primary key (cid)
)engine= innodb;
在JPA的开发过程之中是需要提供有一个持久化类的,而这个 持久化类 需要使用到一些特定的注解进行标记(JPA提供了所有可用的注解),同时这个类的结构要与数据表的结构完全对应。
创建实体类
package look.word.po;
import jakarta.persistence.*;
import lombok.*;
import org.hibernate.Hibernate;
import java.util.Date;
import java.util.Objects;
@Entity // 一个基于JPA规范的实体类
@Table(name = "course") //指定当前实体类关联的表
@Getter
@Setter
@ToString
@RequiredArgsConstructor
public class Course {
@Id // 标识为主键
@GeneratedValue(strategy = GenerationType.IDENTITY) //指定主键生成策略
private Long cid;
// @Column注解,设置属性关联的数据库表字段
// 注意:如果属性名和表字段名相同,可以不设置
private String cname;
@Temporal(TemporalType.DATE) // 定义时间类型
private Date start;
@Temporal(TemporalType.DATE)
private Date end;
private Integer credit;
private Integer num;
// equels() hashCode()
}
常用注解
创建JAP配置文件
resources/META-INF/persistence.xml
注意: 配置很多,但不用记 记得修改数据库,我这里是基于Hikari连接池的,不需要可以直接使用简化版
<persistence version="2.1"
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_1.xsd">
<persistence-unit name="YootkJPA">
<class>look.word.po.Courseclass>
<properties>
<property name="hibernate.connection.provider_class"
value="org.hibernate.hikaricp.internal.HikariCPConnectionProvider"/>
<property name="hibernate.dialect"
value="org.hibernate.dialect.MySQLDialect"/>
<property name="hibernate.hikari.dataSourceClassName"
value="com.zaxxer.hikari.HikariDataSource"/>
<property name="hibernate.hikari.minimumIdle"
value="5"/>
<property name="hibernate.hikari.maximumPoolSize"
value="10"/>
<property name="hibernate.hikari.idleTimeout"
value="3000"/>
<property name="hibernate.hikari.dataSource.driverClassName"
value="com.mysql.cj.jdbc.Driver"/>
<property name="hibernate.hikari.dataSource.jdbcUrl"
value="jdbc:mysql://localhost:3306/yootk"/>
<property name="hibernate.hikari.dataSource.username"
value="root"/>
<property name="hibernate.hikari.dataSource.password"
value="317311"/>
<property name="hibernate.show_sql"
value="true"/>
<property name="hibernate.format_sql"
value="false"/>
properties>
persistence-unit>
persistence>
简化版:
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence" version="2.1">
<persistence-unit name="mysql-jpa">
<properties>
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
<property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/yootk"/>
<property name="hibernate.connection.username" value="root"/>
<property name="hibernate.connection.password" value="317311"/>
<property name="hibernate.format_sql" value="true"/>
properties>
persistence-unit>
persistence>
Hibernate可移植性配置核心: hibernate.dialect, 配置不同的方言就可以实现不同的数据库移植处理
创建日期工具类:
知道用就好,不需要知道其原理。字符串转日期对象
package look.word.util;
import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.util.Date;
/**
* @author : look-word
* 2022-09-19 22:38
**/
public class DateUtil {
/**
* 转换格式
*/
private static final String DATA_PATTERN = "yyyy-MM-dd";
/**
* 日期格式化
*/
private static final DateTimeFormatter DATE_FORMATTER =
DateTimeFormatter.ofPattern(DATA_PATTERN);
private static final ZoneId ZONE_ID = ZoneId.systemDefault();
public static Date stringToDate(String date) {
LocalDate localDate = LocalDate.parse(date, DATE_FORMATTER);
Instant instant = localDate.atStartOfDay().atZone(ZONE_ID).toInstant();
return Date.from(instant);
}
}
测试:
测试文件夹下,创建测试文件,因为我们引入了 Junit 依赖,可以直接使用。
import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
import look.word.po.Course;
import look.word.util.DateUtil;
import org.junit.jupiter.api.Test;
/**
* @author : look-word
* 2022-09-19 22:44
**/
public class TestCoursePersistence {
@Test
public void testAdd() {
// 创建JPA Entity工厂
EntityManagerFactory factory =
Persistence.createEntityManagerFactory("YootkJPA");
// JPA操作对象
EntityManager entityManager = factory.createEntityManager();
// 开启事务
entityManager.getTransaction().begin();
Course course = new Course(); // 创建实体对象
course.setCname("Spring编程实战");
course.setStart(DateUtil.stringToDate("2022-09-19"));
course.setEnd(DateUtil.stringToDate("2022-12-30"));
course.setCredit(2);
course.setNum(88);
entityManager.persist(course); // 类似于插入
entityManager.getTransaction().commit(); // 提交事务
factory.close();// 关闭连接
}
}
// 执行结果 需要往下翻 才能看到
// Hibernate: insert into course (cname, credit, end, num, start) values (?, ?, ?, ?, ?) 执行的sql
// 在JPA配置文件中有配置
一定要及得提交事务。
- 执行错误的话,一定要是上面哪一步出现错误了,请仔细查看
- 执行 没有日志输出,提示log4j日志配置的话,是由于我们没有配置日志信息
**配置日志: **log4j.properties
#将等级为DEBUG的日志信息输出到console和file这两个目的地,console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file
#控制台输出的相关设置
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.Threshold=DEBUG
log4j.appender.console.ImmediateFlush=true
log4j.appender.console.Target=System.err
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=[%-5p] %d(%r) --> [%t] %l: %m %x %n
#文件输出的相关设置
log4j.appender.file = org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./log/logFile.log
log4j.appender.file.MaxFileSize=10mb
log4j.appender.file.Threshold=DEBUG
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=[%p][%d{yy-MM-dd}][%c]%m%n
#日志输出级别
log4j.logger.org.mybatis=DEBUG
log4j.logger.java.sql=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.ResultSet=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG