JPA技术初认识

JPA技术初认识

<?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" transaction-type="RESOURCE_LOCAL">

<!--
配置用什么ORM框架
1. 实际上配置的是 javax.persistence.spi.PersistenceProvider 接口的实现类
2. 如果JPA项目中只有一个JPA的实现产品，则可以不配置该节点
-->
<provider>org.hibernate.ejb.HibernatePersistence</provider>

<class>cn.lamb.jpa.User</class>

<properties>
<!-- 配置数据源信息 -->
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="javax.persistence.jdbc.url" value="jdbc:mysql://127.0.0.1:3306/jpa?charsetEncoding=utf8"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="javax.persistence.jdbc.password" value="ROOT"/>

<!-- 配置JPA实现产品的属性，即hibernate的属性 -->
<property name="hibernate.format_sql" value="true"/><!-- 是否格式化sql语句 -->
<property name="hibernate.show_sql" value="true"/> <!-- 是否在控制台打印sql语句 -->
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
</persistence>

package cn.lamb.jpa;

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="USER")
@Entity
public class User {

private Integer id;
private String name;
private String email;

@Column(name="ID")
@GeneratedValue(strategy=GenerationType.AUTO)
@Id
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
@Column(name="NAME")
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Column(name="EMAIL")
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}

}

package cn.lamb.jpa;

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

public class TEST {

public static void main(String[] args) {
//1. 创建EntityManagerFactory
String persistenceUnitName = "jpa";
EntityManagerFactory factory = Persistence.createEntityManagerFactory(persistenceUnitName);

//2. 创建EntityManager
EntityManager entityManager = factory.createEntityManager();

//3.开启事务
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();

//4. 持久化操作
User user = new User();
user.setName("tom2");
user.setEmail("lamb@qq.com");

//添加user到数据库，相当于hibernate的save();
entityManager.persist(user);

//5. 提交事务
transaction.commit();

//6. 关闭EntityManager
entityManager.close();

//7. 关闭EntityManagerFactory
factory.close();
}
}