mybatis缓存之一级缓存
Posted Kevin-养码青年
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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 [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
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