mybatis缓存之一级缓存（二）

这篇文章介绍下mybatis的一级缓存的生命周期

一级缓存的产生

一级缓存的产生，并不是看mappper的xml文件的select方法，看下面的例子

mapper.xml

<select id="getById" resultType="entity.TempEntity">
select * from  temp where id = #{id}
</select>

test

@Test
public  void testSelectAsUpdate() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
sqlSession.update("dao.Temp03Dao.getById", 1);
sqlSession.update("dao.Temp03Dao.getById", 1);
}

执行结果

2020-06-26 17:33:27,899 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:33:27,922 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:33:27,923 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:33:27,923 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)

我们可以看到执行了2次查询。说明并没有产生缓存。说明和sqlsession调用的方法是有关系的

只有调用上图中的方法才会产生一级缓存

一级缓存的销毁

1.关闭session

这个是根据debug看到的一级缓存的最终结构。下面是整个依赖的类图

test

@Test
public  void test() throws IOException, NoSuchFieldException, IllegalAccessException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity1);

Field executorField = sqlSession.getClass().getDeclaredField("executor");
executorField.setAccessible(true);
CachingExecutor  cachingExecutor = (CachingExecutor) executorField.get(sqlSession);

Field declaredField = cachingExecutor.getClass().getDeclaredField("delegate");
declaredField.setAccessible(true);
SimpleExecutor simpleExecutor  = (SimpleExecutor) declaredField.get(cachingExecutor);

Field localCacheField = simpleExecutor.getClass().getSuperclass().getDeclaredField("localCache");
localCacheField.setAccessible(true);
PerpetualCache perpetualCache = (PerpetualCache) localCacheField.get(simpleExecutor);

Field cacheField = perpetualCache.getClass().getDeclaredField("cache");
cacheField.setAccessible(true);
Map<Object,Object> map= (Map<Object, Object>) cacheField.get(perpetualCache);
logger.info("缓存关闭前");
for (Map.Entry<Object,Object> objectObjectEntry:map.entrySet()){
logger.info(objectObjectEntry.getKey() + "===" + objectObjectEntry.getValue());
}
sqlSession.close();
logger.info("缓存关闭后");

for (Map.Entry<Object,Object> objectObjectEntry:map.entrySet()){
logger.info(objectObjectEntry.getKey() + "=" + objectObjectEntry.getValue());
}
}

运行结果

2020-06-26 17:38:52,777 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:38:52,801 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:38:52,824 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:38:52,824 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:38:52,825 INFO [TempTest] - 缓存关闭前
2020-06-26 17:38:52,826 INFO [TempTest] - -1654591322:461730790:dao.Temp03Dao.getById:0:2147483647:select * from  temp where id = ?:1:dev===[TempEntity{id=1, value1='11111', value2='aaaaa'}]
2020-06-26 17:38:52,827 INFO [TempTest] - 缓存关闭后

可以看到session关闭后，缓存就不存在了

2.Commit提交

test

@Test
public  void testCommit() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity1);
sqlSession.commit();
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);

}

运行结果

2020-06-26 17:40:40,821 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:40:40,846 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:40:40,862 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:40:40,862 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:40:40,863 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:40:40,863 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:40:40,864 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:40:40,864 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:40:40,864 INFO [TempTest] - false

说明sqlSession.commit时会清空缓存

3.Rollback

test

@Test
public  void testRollback() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity1);
sqlSession.rollback();
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);

}

执行结果

2020-06-26 17:42:23,793 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:42:23,833 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:42:23,843 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:42:23,843 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:42:23,844 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:42:23,844 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:42:23,845 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:42:23,845 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:42:23,845 INFO [TempTest] - false

sqlSession.rollback()也会清空缓存

4.update更新

这里是在第一次查询后，紧接着进行update操作。这里与表无关。就是操作其它表，也会清空缓存。

test

@Test
public  void testForUpdate() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity1);
sqlSession.update("dao.Temp03Dao.updateById", 1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);

}

运行结果

2020-06-26 17:45:43,997 DEBUG
200c
[dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:45:44,034 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:45:44,048 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:45:44,049 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:45:44,049 DEBUG [dao.Temp03Dao.updateById] - ==>  Preparing: update temp set value1 = 'ffffff' where id = ?
2020-06-26 17:45:44,049 DEBUG [dao.Temp03Dao.updateById] - ==> Parameters: 1(Integer)
2020-06-26 17:45:44,050 DEBUG [dao.Temp03Dao.updateById] - <==    Updates: 1
2020-06-26 17:45:44,051 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:45:44,051 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:45:44,052 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:45:44,053 INFO [TempTest] - TempEntity{id=1, value1='ffffff', value2='aaaaa'}
2020-06-26 17:45:44,053 INFO [TempTest] - false

这里还是在一个session会话中。记得之前有人给我说只要在一个session会话中，执行update不会清空缓存。这里的代码就证明了

5.clearCache 主动清除

test

@Test
public  void testClearCatch() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity1);
sqlSession.clearCache();
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp03Dao.getById", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);

}

运行结果

2020-06-26 17:48:42,085 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:48:42,110 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:48:42,124 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:48:42,124 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:48:42,125 DEBUG [dao.Temp03Dao.getById] - ==>  Preparing: select * from temp where id = ?
2020-06-26 17:48:42,125 DEBUG [dao.Temp03Dao.getById] - ==> Parameters: 1(Integer)
2020-06-26 17:48:42,126 DEBUG [dao.Temp03Dao.getById] - <==      Total: 1
2020-06-26 17:48:42,126 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 17:48:42,126 INFO [TempTest] - false

一级缓存 脏读问题