JPA学习（一）

一、JPA的helloword实例。

使用Eclipse创建JPA工程，会自动生成persistence.xml文件。

文件的配置如下 ：

<?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_1" transaction-type="RESOURCE_LOCAL">
    <!-- 配置使用什么 ORM产品作为JPA的实现 -->
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <!-- 添加持久化类 -->
    <class>com.jpa.helloword.Customer</class>
    <!-- 连接数据库配置 -->
    <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="root"/>
    
    <!-- 配置JPA实现产品的配置  -->
    <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>

持久化实体类：

/**
 * 
 */
package com.jpa.helloword;

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

/**
 * @author 徐庶
 * @date 2016年12月10日
 */
@Table(name="JPA_CUSTOMERS")
@Entity
public class Customer {

  private  Integer id;
  private String name;
  private String email;
  private int age;
  
  @GeneratedValue(strategy=GenerationType.AUTO)
  @Id
  public Integer getId() {
    return id;
  }
  public void setId(Integer id) {
    this.id = id;
  }
  
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  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;
  }
  
  
}

测试类如下：

/**
 * 
 */
package com.jpa.helloword;

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

import org.junit.Test;

/**
 * @author 徐庶
 * @date 2016年12月10日
 */
public class Main {
  @Test
  public void jpa() {
  //1.创建EntityManagerFactory
    String persistenceUnitName="JPA_1";//该名称就是persistence-unit的name
    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.持久化操作
    Customer customer=new Customer();
    customer.setName("tom");
    customer.setAge(12);
    customer.setEmail("tom@163.com");
    entityManager.persist(customer); //保存
  //5.提交事务
    transaction.commit();
  //6.关闭  entityManager
    entityManager.close();
  //7.关闭 entityManagerFactory
    entityManagerFactory.close();
    
  }
}

该Demo所需要的jar包。

​​点击打开链接​​

JPA的Helloword测试Demo至此完成，该程序运行成功后数据库中会插入一条数据。