JPA学习（五、JPA_二级缓存）

框架学习之JPA（五）

JPA是Java Persistence API的简称，中文名Java持久层API，是JDK 5.0注解或XML描述对象－关系表的映射关系，并将运行期的实体对象持久化到数据库中。

Sun引入新的JPA ORM规范出于两个原因：其一，简化现有Java EE和Java SE应用开发工作；其二，Sun希望整合ORM技术，实现天下归一。

学习视频：尚硅谷框架jpa学习（有兴趣的同学留言邮箱）

使用软件：eclipse

Java版本：jdk8

本节目录

五、JPA_二级缓存

1.添加jar包

2.修改persistence.xml配置文件

3添加ehcache.xml配置文件

4.启动ehcache.xml配置文件，在persistence.xml配置文件中配置

5.需要缓存的类上添加注解

五、JPA_二级缓存

一级缓存：同一个entityManager中不用重复在数据库中查询同一个数据

二级缓存：

• <shared-cache-mode> 节点：若 JPA 实现支持二级缓存，该节点可以配置在当前的持久化单元中是否启用二级缓存，可配置如下值：
  • 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

1.添加jar包

2.修改persistence.xml配置文件

• 查看第四步，防止一的persistence.xml文件

3.添加ehcache.xml配置文件

<ehcache>
    <!-- Sets the path to the directory where cache .data files are created.

         If the path is a Java System Property it is replaced by

         its value in the running VM.

         The following properties are translated:

         user.home - User's home directory

         user.dir - User's current working directory

         java.io.tmpdir - Default temp file path -->

    <diskStore path="java.io.tmpdir"/>

    <!--Default Cache configuration. These will applied to caches programmatically created through

        the CacheManager.

        The following attributes are required for defaultCache:

        maxInMemory       - Sets the maximum number of objects that will be created in memory

        eternal           - Sets whether elements are eternal. If eternal,  timeouts are ignored and the element

                            is never expired.

        timeToIdleSeconds - Sets the time to idle for an element before it expires. Is only used

                            if the element is not eternal. Idle time is now - last accessed time

        timeToLiveSeconds - Sets the time to live for an element before it expires. Is only used

                            if the element is not eternal. TTL is now - creation time

        overflowToDisk    - Sets whether elements can overflow to disk when the in-memory cache

                            has reached the maxInMemory limit.

        -->

    <defaultCache

        maxElementsInMemory="10000"

        eternal="false"

        timeToIdleSeconds="120"

        timeToLiveSeconds="120"

        overflowToDisk="true"

        />

    <!--Predefined caches.  Add your cache configuration settings here.

        If you do not have a configuration for your cache a WARNING will be issued when the

        CacheManager starts

        The following attributes are required for defaultCache:

        name              - Sets the name of the cache. This is used to identify the cache. It must be unique.

        maxInMemory       - Sets the maximum number of objects that will be created in memory

        eternal           - Sets whether elements are eternal. If eternal,  timeouts are ignored and the element

                            is never expired.

        timeToIdleSeconds - Sets the time to idle for an element before it expires. Is only used

                            if the element is not eternal. Idle time is now - last accessed time

        timeToLiveSeconds - Sets the time to live for an element before it expires. Is only used

                            if the element is not eternal. TTL is now - creation time

        overflowToDisk    - Sets whether elements can overflow to disk when the in-memory cache

                            has reached the maxInMemory limit.

        -->

    <!-- Sample cache named sampleCache1

        This cache contains a maximum in memory of 10000 elements, and will expire

        an element if it is idle for more than 5 minutes and lives for more than

        10 minutes.

        If there are more than 10000 elements it will overflow to the

        disk cache, which in this configuration will go to wherever java.io.tmp is

        defined on your system. On a standard Linux system this will be /tmp"

        -->

    <cache name="sampleCache1"

        maxElementsInMemory="10000"

        eternal="false"

        timeToIdleSeconds="300"

        timeToLiveSeconds="600"

        overflowToDisk="true"

        />

    <!-- Sample cache named sampleCache2

        This cache contains 1000 elements. Elements will always be held in memory.

        They are not expired. -->

    <cache name="sampleCache2"

        maxElementsInMemory="1000"

        eternal="true"

        timeToIdleSeconds="0"

        timeToLiveSeconds="0"

        overflowToDisk="false"

        /> -->

    <!-- Place configuration for your caches following -->

</ehcache>

　　

4.启动ehcache.xml配置文件，在persistence.xml配置文件中配置

<?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="SGG-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 javax.persistence.spi.PersistenceProvider

接口的实现类 2. 若 JPA 项目中只有一个 JPA 的实现产品, 则也可以不配置该节点. -->

<provider>org.hibernate.ejb.HibernatePersistence</provider>

<!-- 添加持久化类 -->

<class>hue.edu.xiong.jpa.Customer</class>

<class>hue.edu.xiong.jpa.Order</class>

<class>hue.edu.xiong.jpa.Manager</class>

<class>hue.edu.xiong.jpa.Department</class>

<class>hue.edu.xiong.jpa.Item</class>

<class>hue.edu.xiong.jpa.Category</class>

<!-- 配置二级缓存的策略

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>

<!-- 连接数据库的基本信息 -->

<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="admin" />

<!-- 配置JPA实现产品的基本属性，配置hibernate -->

<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>

　

5.需要缓存的类上添加注解

测试案例：

@Test

public void testSecondLevelCache(){

Customer customer1 = entityManager.find(Customer.class, 1);

transaction.commit();

entityManager.close();

entityManager = entityManagerFactory.createEntityManager();

transaction = entityManager.getTransaction();

transaction.begin();

Customer customer2 = entityManager.find(Customer.class, 1);

}