JPA学习笔记-二级缓存

默认情况下开启一级缓存，如下

@Test
public void testSecondLevelCache() {

User user = entityManager.find(User.class, 1);

System.out.println("------------------");//只发送一条SQL查询语句

User user1 = entityManager.find(User.class, 1);

}

@Test
public void testSecondLevelCache() {
User user = entityManager.find(User.class, 1);
entityTransaction.commit();
entityManager.close();
System.out.println("------------------");
entityManager = entityManagerFactory.createEntityManager();
entityTransaction = entityManager.getTransaction();
entityTransaction.begin();
User user1 = entityManager.find(User.class, 1);
//发送两条查询语句
}

下面配置二级缓存

persistance.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" transaction-type="RESOURCE_LOCAL">

<!-- 配置使用什么ORM产品来作为JPA的实现 1.实际上配置的是javx.persistance.spi.PersistanceProvider接口的实现类
2.若JPA项目中只有一个JPA的实现产品，也可以不配置该节点 -->
<provider>org.hibernate.ejb.HibernatePersistence</provider>

<!-- 添加持久化类 -->
<class>com.jpa.beans.User</class>

<!-- 配置二级缓存策略  -->
<!--
ALL：所有的实体类都被缓存
NONE：所有的实体类都不被缓存.
ENABLE_SELECTIVE：标识 @Cacheable(true) 注解的实体类将被缓存
DISABLE_SELECTIVE：缓存除标识 @Cacheable(false) 以外的所有实体类
UNSPECIFIED：默认值，JPA 产品默认值将被使用
-->

<shared-cache-mode>ENABLE_SELECTIVE</shared-cache-mode>

<properties>
<property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver" />
<property name="javax.persistence.jdbc.url" value="jdbc:mysql:///test" />
<property name="javax.persistence.jdbc.user" value="root" />
<property name="javax.persistence.jdbc.password" value="" />

<!-- 配置JPA实现产品的基本属性，即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" />

<!-- 二级缓存相关 -->
<property name="hibernate.cache.use_second_level_cache" value="true"/>
<property name="hibernate.cache.region.factory_class" value="org.hibernate.cache.ehcache.EhCacheRegionFactory"/>
<property name="hibernate.cache.use_query_cache" value="true"/>
</properties>

</persistence-unit>
</persistence>

加入ehcache相关jar包
ehcache-core-2.4.3.jar
hibernate-ehcache-4.3.5.Final.jar
slf4j-api-1.6.1.jar

加入ehcache.xml（hibernate-release-4.3.5.Final\project\etc目录下）

在实体类上加入Cacheable注解

@Cacheable(true)
@Table(name = "jps_user")
@Entity
public class User {
@GeneratedValue
@Id
private Integer id;
private String username;
private String password;
//getter setter
}

测试

@Test
public void testSecondLevelCache() {
User user = entityManager.find(User.class, 1);
entityTransaction.commit();
entityManager.close();
System.out.println("------------------");
entityManager = entityManagerFactory.createEntityManager();
entityTransaction = entityManager.getTransaction();
entityTransaction.begin();
User user1 = entityManager.find(User.class, 1);

}

以上测试代码只会发送一条SQL查询语句。二级缓存启用成功。

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