JPA实例-转载

具体例子

    完成工程后工程结构如下图：

    

 (注意：persistence.xml文件的位置决定持久性的根(Persistence Root)。持久性的根为JAR文件或者包含META-INF目录（前提是persistence.xml位于此）的目录。一般将这个persistence.xml文件放在src下的META-INF中。命名及位置都不能变)

a)、导入相关jar包（见上图）和创建META-INF和persistence.xml文件.

persistence.xml配置如下：(我用的数据为MySQL,采用不同数据库及JPA的不同实现版本会导致配置内容不同)

   

<persistence 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_version=1">
    <persistence-unit name="mysqlJPA" transaction-type="RESOURCE_LOCAL">
        <properties>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect" />
            <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />
            <property name="hibernate.connection.username" value="root" />
            <property name="hibernate.connection.password" value="123456" />
            <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/db1" />
            <property name="hibernate.max_fetch_depth" value="3" />
            <property name="hibernate.hbm2ddl.auto" value="update" />
        </properties>
    </persistence-unit>
</persistence>

b）、编写实体bean，如下：

   

package com.hmk.bean;

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

@Entity
public class Person {
    private int id;
    private String name;

    @Id @GeneratedValue
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    @Column(length=12)
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

}

   

c）、编写junit测试代码，如下：

  

    

package junit.test;


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

import org.junit.BeforeClass;
import org.junit.Test;

import com.hmk.bean.Person;

public class JpaTest {

    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
    }

    @Test public void createTable(){
        //可以验证生成表是否正确
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        factory.close();
    }

    @Test public void save(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        Person person = new Person(); //person为new状态
        person.setName("zhang san");
        em.persist(person); //持久化实体
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
    //new 、托管、脱管、删除

    @Test public void update(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        Person person = em.find(Person.class, 1);
        person.setName("hmk"); //person为托管状态
        em.getTransaction().commit();
        em.close();
        factory.close();
    }

    @Test public void update2(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        Person person = em.find(Person.class, 1);
        em.clear(); //把实体管理器中的所有实体变为脱管状态
        person.setName("hmk2");
        em.merge(person); //把脱管状态变为托管状态,merge可以自动选择insert or update 数据
        em.getTransaction().commit();
        em.close();
        factory.close();
    }

    @Test public void remove(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        Person person = em.find(Person.class, 1);
        em.remove(person); //删除实体
        em.getTransaction().commit();
        em.close();
        factory.close();
    }

    @Test public void find(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        EntityManager em = factory.createEntityManager();
        Person person = em.find(Person.class, 2); //类似于hibernate的get方法,没找到数据时，返回null
        System.out.println(person.getName());
        em.close();
        factory.close();
    }
    @Test public void find2(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA");
        EntityManager em = factory.createEntityManager();
        Person person = em.getReference(Person.class, 2); //类似于hibernate的load方法,延迟加载.没相应数据时会出现异常
        System.out.println(person.getName()); //真正调用时才查找数据
        em.close();
        factory.close();
    }
}

d）、运行junit测试代码里的相应方法就行可以。