JPA入门实例

比眉伴天荒 2022-06-09 02:20 87阅读 0赞

工程目录：  
![这里写图片描述][SouthEast]

(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包和创建META-INF和persistence.xml文件.

persistence.xml配置如下：

<?xml version="1.0" encoding="UTF-8"?>
    <persistence xmlns="http://java.sun.com/xml/ns/persistence" version="2.0">  
        <persistence-unit name="mysqlJPA" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.ejb.HibernatePersistence</provider> 
        <class>com.jpa.entity.Person</class> 
        <class>com.jpa.entity.UserInfo</class> 
        <class>com.jpa.entity.AccountInfo</class> 
            <properties> 
                <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/> 
                <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/test"/> 
                <property name="hibernate.connection.username" value="root"/> 
                <property name="hibernate.connection.password" value=""/> 
                <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5Dialect"/> 
                <property name="hibernate.show_sql" value="true"/> 
                <property name="hibernate.format_sql" value="true"/> 
                <property name="hibernate.use_sql_comments" value="false"/> 
                <property name="hibernate.hbm2ddl.auto" value="update"/> 
            </properties> 
        </persistence-unit>  
    </persistence>

可以选择性加入spring依赖：

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jpa="http://www.springframework.org/schema/data/jpa" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd">
    
        <context:component-scan base-package="com.jpa"/>
    
        <tx:annotation-driven transaction-manager="transactionManager"/>
    
        <jpa:repositories base-package="com.jpa.dao" repository-impl-postfix="Impl" entity-manager-factory-ref="entityManagerFactory" transaction-manager-ref="transactionManager"/>
    
        <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
            <property name="entityManagerFactory" ref="entityManagerFactory"/>
        </bean>
    
        <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
                <property name="jpaVendorAdapter">
                    <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                    <property name="generateDdl" value="false"/>
                    <property name="showSql" value="true"/>
                </bean>
                </property>
        </bean>
    
    </beans>

b）、编写实体bean，如下：

package com.jpa.entity;
    
    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;  
        }
        @Override
        public String toString() {
            return "Person [id=" + id + ", name=" + name + "]";
        }  
    
    
    }

c）、编写junit测试代码，如下：

package com.jpa.test;
    
    import javax.persistence.EntityManager;
    import javax.persistence.EntityManagerFactory;
    import javax.persistence.Persistence;
    
    import org.hibernate.sql.Update;
    
    import com.jpa.entity.Person;
    import com.jpa.service.UserServiceImpl;
    
    public class JpaTest {
    
    
        public void createTable(){  
            //可以验证生成表是否正确  
            EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA"); 
            factory.close(); 
        }  
    
    
       public static  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  
    
        public static 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(); 
        }  
    
        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(); 
        }  
    
         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(); 
        }  
    
        public static void find(){  
            EntityManagerFactory factory = Persistence.createEntityManagerFactory("mysqlJPA"); 
            EntityManager em = factory.createEntityManager(); 
            Person person = em.find(Person.class, 1); //类似于hibernate的get方法,没找到数据时，返回null 
            System.out.println(person); 
            em.close(); 
            factory.close(); 
        }  
        public static 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(); 
        }  
    
        public static void main(String[] args) {
              find(); 
            //new UserServiceImpl().createNewAccount("ZhangJianPing", "123456", 1); 
        }
    }

[SouthEast]: /images/20220609/bf07403444ac4682b3969b940b1d8dd5.png