1.Mybatis的二级缓存

2.怎样开启Mybatis的二级缓存

3.怎样开启Mybatis的二级缓存

3.1 在MybatisTest.java中测试一级缓存

    /**
     * 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);
        }
    }

3.2 goods.xml中

 <!--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"/>
    

3.3 MybatisTest.java中测试二级缓存

  /**
     * 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);
        }
    }