016.1MyBatis二级缓存（1）

1.一级缓存和二级缓存

 2.缓存的范围

 3.二级缓存的运行规则

 4.测试一级缓存

/**
     * 测试一级缓存
     *
     * @throws Exception
     */
    @Test
    public void testLv1Cache() throws Exception
    {
        SqlSession session = null;
        try
        {
            session = MyBatisUtils.openSession();
            Goods goods = session.selectOne("goods.selectById", 1603);
            Goods goods1 = session.selectOne("goods.selectById", 1603);
            System.out.println(goods.hashCode() + ":" + goods1.hashCode());
        }
        catch (Exception e)
        {
            throw e;
        }
        finally
        {
            MyBatisUtils.closeSession(session);
        }

        try
        {
            session = MyBatisUtils.openSession();
            Goods goods = session.selectOne("goods.selectById", 1603);
            session.commit();//commit提交时对该namespace缓存强制清空
            Goods goods1 = session.selectOne("goods.selectById", 1603);
            System.out.println(goods.hashCode() + ":" + goods1.hashCode());
        }
        catch (Exception e)
        {
            throw e;
        }
        finally
        {
            MyBatisUtils.closeSession(session);
        }
    }

5.开启二级缓存

5.1 goods.xml

<!--开启了二级缓存
        eviction是缓存的清除策略,当缓存对象数量达到上限后,自动触发对应算法对缓存对象清除
            1.LRU – 最近最久未使用:移除最长时间不被使用的对象。
            O1 O2 O3 O4 .. O512
            14 99 83 1     893
            2.FIFO – 先进先出:按对象进入缓存的顺序来移除它们。
            3.SOFT – 软引用:移除基于垃圾收集器状态和软引用规则的对象。
            4.WEAK – 弱引用:更积极的移除基于垃圾收集器状态和弱引用规则的对象。
    -->
    <cache eviction="LRU" flushInterval="600000" size="512" readOnly="true"/>

5.2测试用例

/**
     * 测试二级缓存
     *
     * @throws Exception
     */
    @Test
    public void testLv2Cache() throws Exception
    {
        SqlSession session = null;
        try
        {
            session = MyBatisUtils.openSession();
            Goods goods = session.selectOne("goods.selectById", 1603);
            System.out.println(goods.hashCode());
        }
        catch (Exception e)
        {
            throw e;
        }
        finally
        {
            MyBatisUtils.closeSession(session);
        }

        try
        {
            session = MyBatisUtils.openSession();
            Goods goods = session.selectOne("goods.selectById", 1603);
            System.out.println(goods.hashCode());
        }
        catch (Exception e)
        {
            throw e;
        }
        finally
        {
            MyBatisUtils.closeSession(session);
        }
    }