Hibernate二级缓存配置

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一、没有配置二级缓存情形

    @Test    public void test(){        Employee employee = (Employee) session.get(Employee.class, 1);        Employee employee2 = (Employee) session.get(Employee.class, 1);        System.out.println(employee);        System.out.println(employee2);    }

因为hibernate缓存的原因，实际上只会发送一条sql语句。

现在再来实验一下，得到employee2前清楚session缓存

    @Test    public void test2(){        Employee employee = (Employee) session.get(Employee.class, 1);        session.clear();        Employee employee2 = (Employee) session.get(Employee.class, 1);        System.out.println(employee);        System.out.println(employee2);    }

Hibernate:     select        employee0_.ID as ID1_1_0_,        employee0_.NAME as NAME2_1_0_,        employee0_.DEPT_ID as DEPT_ID3_1_0_     from        EMPLOYEES employee0_     where        employee0_.ID=?Hibernate:     select        employee0_.ID as ID1_1_0_,        employee0_.NAME as NAME2_1_0_,        employee0_.DEPT_ID as DEPT_ID3_1_0_     from        EMPLOYEES employee0_     where        employee0_.ID=?Employee [id=1]Employee [id=1]

我们看到发送了两条sql语句。

再来看另一种情形

@Test    public void test3(){        Employee employee = (Employee) session.get(Employee.class, 1);        session.close();        session = sessionFactory.openSession();        Employee employee2 = (Employee) session.get(Employee.class, 1);        System.out.println(employee);        System.out.println(employee2);    }

第二次get之前关闭session，然后开启一个session,前后两个session是不一样的。这样发送了两条select语句。问题：可不可以开启两个不同的session时，如果是相同的OID，则只发送一条sql语句，即对于不同的session，hibernate仍然能够缓存？

答案是配置二级缓存。sessionFactory级别。

2、配置hibernate的二级缓存
(1)导入相应的jra包
ehcache-core-2.4.3.jar
hibernate-ehcache-4.2.4.Final.jar
slf4j-api-1.6.1.jar
(2)配置ehcache.xml文件—使用默认的配置

(3)配置hibernate.cfg.xml文件
①. 启用二级缓存

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

②.配置使用的二级缓存的产品

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

③.配置启用二级缓存的类

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

再执行test3方法时，我们可以看到只发送了一条sql语句。hibernate二级缓存起作用了。

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