认识JPA以及如何使用JPA（1）

一：JDBC是什么？

JDBC统一了Java应用程序访问数据库的标准。

二：什么是JPA?

JPA统一了Java应用程序使用使用ORM框架的方式。

配置文件说明：

三：使用JPA的第一个实例。

1.创建JPA项目，也可以直接创建java项目，然后创建persistence.xml文件

2.导入jar包

3.persistence.xml ：

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
    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">
    <persistence-unit name="Jpa-01" transaction-type="RESOURCE_LOCAL">
        <!-- 配置使用什么ORM产品作为JPA的实现
        1.实际上配置的是javax.persistence.spi.PersistenceProvider接口的实现类
        2.若JPA项目中只有一个JPA的实现产品，则也可以不配置该节点
        -->
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <!-- 添加持久化类 -->
        <class>com.atguigu.jpa.helloworld.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>
            <property name = "javax.persistence.jdbc.url" value="jdbc:mysql:///jpa"></property>
            <property name = "javax.persistence.jdbc.user" value="root"></property>
            <property name = "javax.persistence.jdbc.password" value="root"></property>
            <!-- 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>

4.创建实体类：

package com.atguigu.jpa.helloworld;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Table(name = "JPA_CUSTOMERS")
@Entity
public class Customer {

    private Integer id;
    private String lastName;
    private String email;
    private int age;

    @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 int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }

}

5.测试类：

package com.atguigu.jpa.helloworld;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

public class Main {

    public static void main(String[] args) {
        //1.创建EntitymanagerFactory
        String persistenceUnitName = "Jpa-01";
        EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory(persistenceUnitName);
        //2.创建EntityManager
        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@atguigu.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();
    }

}

6.整体结构：

7.运行

四月 21, 2019 9:44:19 上午 org.hibernate.annotations.common.Version <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {4.0.2.Final}
四月 21, 2019 9:44:19 上午 org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {4.2.4.Final}
四月 21, 2019 9:44:19 上午 org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
四月 21, 2019 9:44:19 上午 org.hibernate.cfg.Environment buildBytecodeProvider
INFO: HHH000021: Bytecode provider name : javassist
四月 21, 2019 9:44:20 上午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000402: Using Hibernate built-in connection pool (not for production use!)
四月 21, 2019 9:44:20 上午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000115: Hibernate connection pool size: 20
四月 21, 2019 9:44:20 上午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000006: Autocommit mode: true
四月 21, 2019 9:44:20 上午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000401: using driver [com.mysql.jdbc.Driver] at URL [jdbc:mysql:///jpa]
四月 21, 2019 9:44:20 上午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
INFO: HHH000046: Connection properties: {user=root, password=****, autocommit=true, release_mode=auto}
四月 21, 2019 9:44:20 上午 org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.MySQLDialect
四月 21, 2019 9:44:20 上午 org.hibernate.engine.jdbc.internal.LobCreatorBuilder useContextualLobCreation
INFO: HHH000423: Disabling contextual LOB creation as JDBC driver reported JDBC version [3] less than 4
四月 21, 2019 9:44:20 上午 org.hibernate.engine.transaction.internal.TransactionFactoryInitiator initiateService
INFO: HHH000268: Transaction strategy: org.hibernate.engine.transaction.internal.jdbc.JdbcTransactionFactory
四月 21, 2019 9:44:20 上午 org.hibernate.hql.internal.ast.ASTQueryTranslatorFactory <init>
INFO: HHH000397: Using ASTQueryTranslatorFactory
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000228: Running hbm2ddl schema update
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000102: Fetching database metadata
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000396: Updating schema
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.DatabaseMetadata getTableMetadata
INFO: HHH000262: Table not found: JPA_CUSTOMERS
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.DatabaseMetadata getTableMetadata
INFO: HHH000262: Table not found: JPA_CUSTOMERS
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.DatabaseMetadata getTableMetadata
INFO: HHH000262: Table not found: JPA_CUSTOMERS
四月 21, 2019 9:44:22 上午 org.hibernate.tool.hbm2ddl.SchemaUpdate execute
INFO: HHH000232: Schema update complete
Hibernate:
    insert
    into
        JPA_CUSTOMERS
        (age, email, LAST_NAME)
    values
        (?, ?, ?)
四月 21, 2019 9:44:22 上午 org.hibernate.service.jdbc.connections.internal.DriverManagerConnectionProviderImpl stop
INFO: HHH000030: Cleaning up connection pool [jdbc:mysql:///jpa]

8.查看表结构

9.完成