Hibernate 的 二级缓存

//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~二级缓存~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/**
*一.  缓存(Cache):
* 		①. 计算机领域非常通用的概念。它介于应用程序和永久性数据存储源(如硬盘上的文件或者数据库)之间，
* 		         其作用是降低应用程序直接读写永久性数据存储源的频率，从而提高应用的运行性能。缓存中的数据是
* 		          数据存储源中数据的拷贝。
* 		②. 缓存的物理介质通常是内存
*
*二.  Hibernate中提供了两个级别的缓存
* 		①. 第一级别的缓存是 Session 级别的缓存，它是属于事务范围的缓存。这一级别的缓存由 hibernate管理的。
*
* 		②. 第二级别的缓存是 SessionFactory 级别的缓存，它是属于进程范围的缓存.其有可分为两中：
* 				内置缓存: Hibernate 自带的, 不可卸载. 通常在 Hibernate 的初始化阶段,
* 					   Hibernate 会把映射元数据和预定义的 SQL 语句放到 SessionFactory 的
* 					         缓存中, 映射元数据是映射文件中数据（.hbm.xml 文件中的数据）的复制.
* 					        该内置缓存是只读的
* 				外置缓存(二级缓存): 一个可配置的缓存插件. 在默认情况下,SessionFactory 不会启用这个缓存插件.
* 							       外置缓存中的数据是数据库数据的复制, 外置缓存的物理介质可以是内存或硬盘
*
* 二级缓存使用范围
* 		使用 Hibernate 的二级缓存：
* 			①. 适合放入二级缓存中的数据:
* 						a.很少被修改
* 						b.不是很重要的数据, 允许出现偶尔的并发问题
*
* 			②. 不适合放入二级缓存中的数据：
* 						a.经常被修改
* 						b.财务数据, 绝对不允许出现并发问题
* 						c.与其他应用程序共享的数据
* 如何使用二级缓存？
*
*
*
*
*/

使用 Hibernate 二级缓存的步骤:

1). 加入二级缓存插件的 jar 包及配置文件:

I. 复制 \hibernate-release-4.2.4.Final\lib\optional\ehcache\*.jar 到当前 Hibrenate 应用的类路径下.

II. 复制 hibernate-release-4.2.4.Final\project\etc\ehcachexml到当前 WEB 应用的类路径下

2). 配置 hibernate.cfg.xml

I. 配置启用 hibernate 的二级缓存

<property name="cache.use_second_level_cache">true</property>

II. 配置hibernate二级缓存使用的产品

<property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>

III. 配置对哪些类使用 hibernate 的二级缓存

类级别的二级缓存配置方式有两种：

方式一： 在hibernate.cfg.xml 中配置

<class-cache usage="read-write" class="com.baidu.QBC_or_LocalSQL.Employee"/>

方式二： 在对象关系映射文件中配置

<hibernate-mapping package="com.baidu.QBC_or_LocalSQL">

<class name="Employee" table="BB_EMPLOYEES">

<!-- 配置二级缓存策略 -->
<cache usage="read-write"/>

<id name="id" type="java.lang.Integer">
<column name="ID" />
<generator class="native" />
</id>

<property name="name" type="java.lang.String">
<column name="NAME" />
</property>

<property name="salary" type="float">
<column name="SALARY" />
</property>

<property name="email" type="java.lang.String">
<column name="EMAIL" />
</property>

<many-to-one name="dept" class="Department" >
<column name="DEPT_ID" />
</many-to-one>

</class>

</hibernate-mapping>

集合别的二级缓存配置方式有两种：

方式一： 在hibernate.cfg.xml 中配置

<collection-cache usage="read-write" collection="com.baidu.QBC_or_LocalSQL.Department.emps"/>

方式二： 在对象关系映射文件中配置

<hibernate-mapping package="com.baidu.QBC_or_LocalSQL">

<class name="Department" table="BB_DEPARTMENTS">

<id name="id" type="java.lang.Integer">
<column name="ID" />
<generator class="sequence" >
<param name="sequence">user_deptid</param>
</generator>
</id>

<property name="name" type="java.lang.String">
<column name="NAME" />
</property>

<set name="emps" table="BB_EMPLOYEES" inverse="true" lazy="true">
<!-- 配置集合级别的二级缓存策略
-->
<cache usage="read-write"/>
<key>
<column name="DEPT_ID" />
</key>
<one-to-many class="Employee" />
</set>

</class>

</hibernate-mapping>

类级别的缓存

使用方式二 的方式配置Employee 的缓存策略

//类级别的缓存
@Test
public void testHibernateClassSecondLevelCache(){

Employee employee = (Employee) session.get(Employee.class, 100);
System.out.println(employee.getName());
transaction.commit();
session.close();

session = sessionFactory.openSession();
transaction = session.beginTransaction();

Employee employee2 = (Employee) session.get(Employee.class, 100);
System.out.println(employee2.getName());
}

未配置二级缓存发送的SQL

Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
King
Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
King

配置二级缓存以后[b]发送的SQL[/b]

Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
King
King

集合缓存

//集合缓存
@Test
public void testHibernateCollectionSecondLevelCache(){
Department dept = (Department) session.get(Department.class, 80);
System.out.println(dept.getName());
System.out.println(dept.getEmps().size());

transaction.commit();
session.close();

session = sessionFactory.openSession();
transaction = session.beginTransaction();

Department dept2 = (Department) session.get(Department.class, 80);
System.out.println(dept2.getName());
System.out.println(dept2.getEmps().size());
}

未配置二级缓存[b]发送的SQL[/b]

Hibernate:
select
department0_.ID as ID1_0_0_,
department0_.NAME as NAME2_0_0_
from
BB_DEPARTMENTS department0_
where
department0_.ID=?
Sales
Hibernate:
select
emps0_.DEPT_ID as DEPT_ID5_0_1_,
emps0_.ID as ID1_1_1_,
emps0_.ID as ID1_1_0_,
emps0_.NAME as NAME2_1_0_,
emps0_.SALARY as SALARY3_1_0_,
emps0_.EMAIL as EMAIL4_1_0_,
emps0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES emps0_
where
emps0_.DEPT_ID=?
34
Hibernate:
select
department0_.ID as ID1_0_0_,
department0_.NAME as NAME2_0_0_
from
BB_DEPARTMENTS department0_
where
department0_.ID=?
Sales
Hibernate:
select
emps0_.DEPT_ID as DEPT_ID5_0_1_,
emps0_.ID as ID1_1_1_,
emps0_.ID as ID1_1_0_,
emps0_.NAME as NAME2_1_0_,
emps0_.SALARY as SALARY3_1_0_,
emps0_.EMAIL as EMAIL4_1_0_,
emps0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES emps0_
where
emps0_.DEPT_ID=?
34

配置二级缓存以后 但是没有配置Employee 的缓存 [b]发送的SQL[/b]

使用方式一 ：在hibernate.cfg.xml

<!--配置 哪个类使用二级缓存
-->
<class-cache usage="read-write" class="com.baidu.QBC_or_LocalSQL.Department"/>
<collection-cache usage="read-write" collection="com.baidu.QBC_or_LocalSQL.Department.emps"/>

Hibernate:
select
department0_.ID as ID1_0_0_,
department0_.NAME as NAME2_0_0_
from
BB_DEPARTMENTS department0_
where
department0_.ID=?
Sales
Hibernate:
select
emps0_.DEPT_ID as DEPT_ID5_0_1_,
emps0_.ID as ID1_1_1_,
emps0_.ID as ID1_1_0_,
emps0_.NAME as NAME2_1_0_,
emps0_.SALARY as SALARY3_1_0_,
emps0_.EMAIL as EMAIL4_1_0_,
emps0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES emps0_
where
emps0_.DEPT_ID=?
34
Sales
Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?

........省略中间的...

Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
Hibernate:
select
employee0_.ID as ID1_1_0_,
employee0_.NAME as NAME2_1_0_,
employee0_.SALARY as SALARY3_1_0_,
employee0_.EMAIL as EMAIL4_1_0_,
employee0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES employee0_
where
employee0_.ID=?
34

配置Employee 的缓存后[b]发送的SQL[/b]

<!--配置 哪个类使用二级缓存
-->
<class-cache usage="read-write" class="com.baidu.QBC_or_LocalSQL.Employee"/>
<class-cache usage="read-write" class="com.baidu.QBC_or_LocalSQL.Department"/>
<collection-cache usage="read-write" collection="com.baidu.QBC_or_LocalSQL.Department.emps"/>

Hibernate:
select
department0_.ID as ID1_0_0_,
department0_.NAME as NAME2_0_0_
from
BB_DEPARTMENTS department0_
where
department0_.ID=?
Sales
Hibernate:
select
emps0_.DEPT_ID as DEPT_ID5_0_1_,
emps0_.ID as ID1_1_1_,
emps0_.ID as ID1_1_0_,
emps0_.NAME as NAME2_1_0_,
emps0_.SALARY as SALARY3_1_0_,
emps0_.EMAIL as EMAIL4_1_0_,
emps0_.DEPT_ID as DEPT_ID5_1_0_
from
BB_EMPLOYEES emps0_
where
emps0_.DEPT_ID=?
34
Sales
34

查询缓存

//查询缓存
@Test
public void testHibernateQuerySecondLevelCache(){
Query query = session.createQuery("FROM Employee");

List<Employee> emps = query.list();
System.out.println(emps.size());

emps = query.list();
System.out.println(emps.size());

/**
* 上面的查询语句和下面的效果一样
* 	Criteria criteria = session.createCriteria(Employee.class);
* 	criteria.setCacheable(true);
*
* 	List<Employee> emps = criteria.list();
* 	System.out.println(emps.size());
*
* 	emps = criteria.list();
* 	System.out.println(emps.size());
*
*/
}

未配置二级缓存[b]发送的SQL[/b]

Hibernate:
select
employee0_.ID as ID1_1_,
employee0_.NAME as NAME2_1_,
employee0_.SALARY as SALARY3_1_,
employee0_.EMAIL as EMAIL4_1_,
employee0_.DEPT_ID as DEPT_ID5_1_
from
BB_EMPLOYEES employee0_
107
Hibernate:
select
employee0_.ID as ID1_1_,
employee0_.NAME as NAME2_1_,
employee0_.SALARY as SALARY3_1_,
employee0_.EMAIL as EMAIL4_1_,
employee0_.DEPT_ID as DEPT_ID5_1_
from
BB_EMPLOYEES employee0_
107

配置二级查询缓存以后

① 在hibernate.cfg.xml 中配置

<!-- 启用查询缓存
-->
<property name="hibernate.cache.use_query_cache">true</property>

② 在测试方法中添加

//设置query 是可以被缓存的
query.setCacheable(true);

//查询缓存
@Test
public void testHibernateQuerySecondLevelCache(){
Query query = session.createQuery("FROM Employee");
//设置query 是可以被缓存的
query.setCacheable(true);

List<Employee> emps = query.list();
System.out.println(emps.size());

emps = query.list();
System.out.println(emps.size());

/**
* 上面的查询语句和下面的效果一样
* 	Criteria criteria = session.createCriteria(Employee.class);
* 	criteria.setCacheable(true);
*
* 	List<Employee> emps = criteria.list();
* 	System.out.println(emps.size());
*
* 	emps = criteria.list();
* 	System.out.println(emps.size());
*
*/
}

[b]发送的SQL[/b]

运行结果：

Hibernate:
select
employee0_.ID as ID1_1_,
employee0_.NAME as NAME2_1_,
employee0_.SALARY as SALARY3_1_,
employee0_.EMAIL as EMAIL4_1_,
employee0_.DEPT_ID as DEPT_ID5_1_
from
BB_EMPLOYEES employee0_
107
107

更新时间戳缓存

//更新时间戳缓存
@Test
public void testHibernateUpdateTimeStamStampCache(){
Query query = session.createQuery("FROM Employee");
query.setCacheable(true);

List<Employee> emps = query.list();
System.out.println(emps.size());

Employee employee = (Employee) session.get(Employee.class, 100);
employee.setSalary(25600);

emps = query.list();
System.out.println(emps.size());

}

更新employeeId =100 的 salary = 25600
发送的SQL

Hibernate:
select
employee0_.ID as ID1_1_,
employee0_.NAME as NAME2_1_,
employee0_.SALARY as SALARY3_1_,
employee0_.EMAIL as EMAIL4_1_,
employee0_.DEPT_ID as DEPT_ID5_1_
from
BB_EMPLOYEES employee0_
107
Hibernate:
update
BB_EMPLOYEES
set
NAME=?,
SALARY=?,
EMAIL=?,
DEPT_ID=?
where
ID=?
Hibernate:
select
employee0_.ID as ID1_1_,
employee0_.NAME as NAME2_1_,
employee0_.SALARY as SALARY3_1_,
employee0_.EMAIL as EMAIL4_1_,
employee0_.DEPT_ID as DEPT_ID5_1_
from
BB_EMPLOYEES employee0_
107

再一次运行

[b]发送的SQL

[/b]

Hibernate:
select
employee0_.ID as ID1_1_,
employee0_.NAME as NAME2_1_,
employee0_.SALARY as SALARY3_1_,
employee0_.EMAIL as EMAIL4_1_,
employee0_.DEPT_ID as DEPT_ID5_1_
from
BB_EMPLOYEES employee0_
107
107

详解 见上面

1. 使用 Hibernate 二级缓存的步骤:

1). 加入二级缓存插件的 jar 包及配置文件:

I. 复制 \hibernate-release-4.2.4.Final\lib\optional\ehcache\*.jar 到当前 Hibrenate 应用的类路径下.
II. 复制 hibernate-release-4.2.4.Final\project\etc\ehcachexml 到当前 WEB 应用的类路径下

2). 配置 hibernate.cfg.xml

I.   配置启用 hibernate 的二级缓存
<property name="cache.use_second_level_cache">true</property>

II.  配置hibernate二级缓存使用的产品
<property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>

2. 配置对哪些类使用 hibernate 的二级缓存
<class-cache usage="read-write" class="com.atguigu.hibernate.entities.Employee"/>

实际上也可以在 .hbm.xml 文件中配置对哪些类使用二级缓存, 及二级缓存的策略是什么.

3. 集合级别的二级缓存的配置

I. 配置对集合使用二级缓存

<collection-cache usage="read-write" collection="com.atguigu.hibernate.entities.Department.emps"/>

也可以在 .hbm.xml 文件中进行配置

<set name="emps" table="GG_EMPLOYEE" inverse="true" lazy="true">
<cache usage="read-write"/>
<key>
<column name="DEPT_ID" />
</key>
<one-to-many class="com.atguigu.hibernate.entities.Employee" />
</set>

II. 注意: 还需要配置集合中的元素对应的持久化类也使用二级缓存! 否则将会多出 n 条 SQL 语句.
<class-cache usage="read-write" class="com.baidu.QBC_or_LocalSQL.Employee"/>
<class-cache usage="read-write" class="com.baidu.QBC_or_LocalSQL.Department"/>
<collection-cache usage="read-write" collection="com.baidu.QBC_or_LocalSQL.Department.emps"/>

4. ehcache 的 配置文件: ehcache.xml
<ehcache>

<!--指定一个目录：当 EHCache 把数据写到硬盘上时, 将把数据写到这个目录下. -->
<diskStore path="d:\\javastudy\test"/>

<!--
设置缓存的默认数据过期策略

maxElementsInMemory: 设置基于内存的缓存中可存放的对象最大数目

eternal: 			设置对象是否为永久的, true表示永不过期,此时将忽略timeToIdleSeconds
和 timeToLiveSeconds属性;
默认值是false

timeToIdleSeconds:	设置对象空闲最长时间,以秒为单位, 超过这个时间,对象过期。当对象过期时,EHCache会把它
从缓存中清除。如果此值为0,表示对象可以无限期地处于空闲状态。

timeToLiveSeconds:	设置对象生存最长时间,超过这个时间,对象过期。如果此值为0,表示对象可以无限期地存在于缓存中.
该属性值必须大于或等于 timeToIdleSeconds 属性值

overflowToDisk:设置基于内存的缓存中的对象数目达到上限后,是否把溢出的对象写到基于硬盘的缓存中

-->
<defaultCache
maxElementsInMemory="10000"
eternal="false"
timeToIdleSeconds="120"
timeToLiveSeconds="120"
overflowToDisk="true"
/>

<!--
设定具体的命名缓存的数据过期策略。每个命名缓存代表一个缓存区域
缓存区域(region)：一个具有名称的缓存块，可以给每一个缓存块设置不同的缓存策略。
如果没有设置任何的缓存区域，则所有被缓存的对象，都将使用默认的缓存策略。即：<defaultCache.../>
Hibernate 在不同的缓存区域保存不同的类/集合。
对于类而言，区域的名称是类名。如:com.atguigu.domain.Customer
对于集合而言，区域的名称是类名加属性名。如com.atguigu.domain.Customer.orders
-->
<!--  name: 设置缓存的名字,它的取值为类的全限定名或类的集合的名字 -->
<cache name="com.baidu.QBC_or_LocalSQL.Employee"
maxElementsInMemory="1"
eternal="false"
timeToIdleSeconds="300"
timeToLiveSeconds="600"
overflowToDisk="true"
/>

<cache name="com.baidu.QBC_or_LocalSQL.Department.emps"
maxElementsInMemory="1000"
eternal="true"
timeToIdleSeconds="0"
timeToLiveSeconds="0"
overflowToDisk="false"
/>

</ehcache>

5.  查询缓存: 默认情况下, 设置的缓存对 HQL 及 QBC 查询时无效的, 但可以通过以下方式使其是有效的

I.  在 hibernate 配置文件中声明开启查询缓存

<property name="cache.use_query_cache">true</property>

II. 调用 Query 或 Criteria 的 setCacheable(true) 方法

III. 查询缓存依赖于二级缓存