Mybatis 一级缓存和引发的问题

爱被打了一巴掌 2022-01-11 05:33 478阅读 0赞

1.Mybatis 是默认开启一级缓存的。跟Spring结合使用的话执行的方法必须**开启事务**一级缓存才有效。  
2.当查询数据时候，先从缓存中寻找是否存在该条数据，存在就直接取出来，不存在，向数据库发送sql查询， 然后将查询后的数据存入缓存返回给程序。

**下边围绕着如下几个问题展开验证：**

1.  开启事务，一级缓存有效
2.  不开启事务，一级缓存失效
3.  Mybatis一级缓存的坑在哪呢？
4.  验证一个事物中进行insert update delete 会刷新一级缓存

**二 验证**

1.开启事务，一级缓存有效。从日志看到确实只执行了一次查询。

@Test
    @Transactional
    public void test() { 
    	LangUser langUser = langUserMapper.selectByPrimaryKey(-1);
    	LangUser langUser1 = langUserMapper.selectByPrimaryKey(-1);
    	LangUser langUser2 = langUserMapper.selectByPrimaryKey(-1);
    
    }

15:58:20.584 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Creating a new SqlSession
    15:58:20.594 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@63648ee9]
    15:58:21.095 [main] WARN  com.alibaba.druid.pool.DruidDataSource - removeAbandoned is true, not use in productiion.
    15:58:21.872 [main] INFO  com.alibaba.druid.pool.DruidDataSource - { dataSource-1} inited
    15:58:21.899 [main] DEBUG org.mybatis.spring.transaction.SpringManagedTransaction - JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@4351171a] will be managed by Spring
    15:58:21.902 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==>  Preparing: select ID, NAME, AGE, SCORE from LANG_USER where ID = ? 
    15:58:21.974 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==> Parameters: -1(Integer)
    15:58:22.013 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==    Columns: ID, NAME, AGE, SCORE
    15:58:22.020 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==        Row: -1, 小狼, 18, 100
    15:58:22.022 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==      Total: 1
    15:58:22.024 [main] DEBUG com.alibaba.druid.pool.PreparedStatementPool - { conn-10004, pstmt-20000} enter cache

2.不开启事务，一级缓存失效

@Test
    public void test() { 
    	LangUser langUser = langUserMapper.selectByPrimaryKey(-1);
    	LangUser langUser1 = langUserMapper.selectByPrimaryKey(-1);
    	LangUser langUser2 = langUserMapper.selectByPrimaryKey(-1);
    }

注意看日志打印,下面这句话执行了出现了三次，每一次查询都创建了一个sqlSeesion，sql也执行了三次。

16:02:29.606 \[main\] DEBUG org.mybatis.spring.SqlSessionUtils - Creating a new SqlSession

16:02:29.606 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Creating a new SqlSession
    16:02:29.612 [main] DEBUG org.mybatis.spring.SqlSessionUtils - SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@4c6daf0] was not registered for synchronization because synchronization is not active
    16:02:29.863 [main] WARN  com.alibaba.druid.pool.DruidDataSource - removeAbandoned is true, not use in productiion.
    16:02:31.175 [main] INFO  com.alibaba.druid.pool.DruidDataSource - { dataSource-1} inited
    16:02:31.224 [main] DEBUG org.mybatis.spring.transaction.SpringManagedTransaction - JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@3088660d] will not be managed by Spring
    16:02:31.230 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==>  Preparing: select ID, NAME, AGE, SCORE from LANG_USER where ID = ? 
    16:02:31.335 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==> Parameters: -1(Integer)
    16:02:31.397 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==    Columns: ID, NAME, AGE, SCORE
    16:02:31.409 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==        Row: -1, 小狼, 18, 100
    16:02:31.413 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==      Total: 1
    16:02:31.414 [main] DEBUG com.alibaba.druid.pool.PreparedStatementPool - { conn-10004, pstmt-20000} enter cache
    16:02:31.417 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@4c6daf0]
    16:02:31.420 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Creating a new SqlSession
    16:02:31.422 [main] DEBUG org.mybatis.spring.SqlSessionUtils - SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@272a179c] was not registered for synchronization because synchronization is not active
    16:02:31.423 [main] DEBUG org.mybatis.spring.transaction.SpringManagedTransaction - JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@3088660d] will not be managed by Spring
    16:02:31.425 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==>  Preparing: select ID, NAME, AGE, SCORE from LANG_USER where ID = ? 
    16:02:31.426 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==> Parameters: -1(Integer)
    16:02:31.430 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==    Columns: ID, NAME, AGE, SCORE
    16:02:31.430 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==        Row: -1, 小狼, 18, 100
    16:02:31.431 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==      Total: 1
    16:02:31.435 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@272a179c]
    16:02:31.435 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Creating a new SqlSession
    16:02:31.437 [main] DEBUG org.mybatis.spring.SqlSessionUtils - SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@67207d8a] was not registered for synchronization because synchronization is not active
    16:02:31.438 [main] DEBUG org.mybatis.spring.transaction.SpringManagedTransaction - JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@3088660d] will not be managed by Spring
    16:02:31.439 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==>  Preparing: select ID, NAME, AGE, SCORE from LANG_USER where ID = ? 
    16:02:31.442 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==> Parameters: -1(Integer)
    16:02:31.444 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==    Columns: ID, NAME, AGE, SCORE
    16:02:31.444 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==        Row: -1, 小狼, 18, 100
    16:02:31.444 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==      Total: 1
    16:02:31.445 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@67207d8a]
    16:02:31.480 [Thread-1] INFO  com.alibaba.druid.pool.DruidDataSource - { dataSource-0} closing ...
    16:02:31.484 [Thread-1] INFO  com.alibaba.druid.pool.DruidDataSource - { dataSource-1} closing ...
    16:02:31.589 [Thread-1] INFO  com.alibaba.druid.pool.DruidDataSource - { dataSource-1} closed

3.**坑在哪呢？我们看这种开启事务的情况。**

第一次查询后，我只是把查询出来的对象赋值“喜洋洋”，我并没有跟数据库有任何交互，下面的两次查询结果竟然修改后的“喜洋洋”。

@Test
    @Transactional
    public void test() { 
    	LangUser langUser = langUserMapper.selectByPrimaryKey(-1);
    	logger.info("姓名："+langUser.getName());
    	langUser.setName("喜洋洋");
    	LangUser langUser1 = langUserMapper.selectByPrimaryKey(-1);
    	logger.info("姓名："+langUser1.getName());
    	LangUser langUser2 = langUserMapper.selectByPrimaryKey(-1);
    	logger.info("姓名："+langUser2.getName());
    }

16:16:22.983 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Creating a new SqlSession
    16:16:22.991 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Registering transaction synchronization for SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@117e0fe5]
    16:16:23.437 [main] WARN  com.alibaba.druid.pool.DruidDataSource - removeAbandoned is true, not use in productiion.
    16:16:24.423 [main] INFO  com.alibaba.druid.pool.DruidDataSource - { dataSource-1} inited
    16:16:24.459 [main] DEBUG org.mybatis.spring.transaction.SpringManagedTransaction - JDBC Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@3c2772d1] will be managed by Spring
    16:16:24.463 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==>  Preparing: select ID, NAME, AGE, SCORE from LANG_USER where ID = ? 
    16:16:24.575 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - ==> Parameters: -1(Integer)
    16:16:24.604 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==    Columns: ID, NAME, AGE, SCORE
    16:16:24.612 [main] TRACE com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==        Row: -1, 小狼, 18, 100
    16:16:24.615 [main] DEBUG com.hao.xu.lang.mapper.oracle.LangUserMapper.selectByPrimaryKey - <==      Total: 1
    16:16:24.617 [main] DEBUG com.alibaba.druid.pool.PreparedStatementPool - { conn-10004, pstmt-20000} enter cache
    16:16:24.618 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Releasing transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@117e0fe5]
    16:16:24.618 [main] INFO  com.hao.xu.lang.mapper.oracle.LangUserMapperTest - 姓名：小狼
    16:16:24.620 [main] INFO  com.hao.xu.lang.mapper.oracle.LangUserMapperTest - 姓名：喜洋洋
    16:16:24.621 [main] INFO  com.hao.xu.lang.mapper.oracle.LangUserMapperTest - 姓名：喜洋洋
    16:16:24.622 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Transaction synchronization deregistering SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@117e0fe5]
    16:16:24.623 [main] DEBUG org.mybatis.spring.SqlSessionUtils - Transaction synchronization closing SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@117e0fe5]

**原因：**  
当数据库建立一次连接，就会创建一个SqlSession对象，默认是DefaultSqlSession这个实现，这个对象给用户提供了操作数据库的各种方法，与此同时，也会创建一个Executor执行器，缓存信息就是维护在Executor中，如果这个sqlSessio进行  
insert update delete 它会释放掉Executor中的缓存

4.验证一个事物中进行insert update delete 会刷新一级缓存

@Test
    @Transactional
    public void test() { 
    	LangUser langUser = langUserMapper.selectByPrimaryKey(-1);
    	logger.info("姓名："+langUser.getName());
    	langUser.setName("喜洋洋");
    
        //新建对象插入表中，让sqlsession 有提交动作
    	LangUser langUser3 = new LangUser();
    	langUser3.setName("红太狼");
    	langUser3.setAge(5);
    	langUser3.setScore("90");
    	langUserMapper.insert(langUser3);
    
    	LangUser langUser1 = langUserMapper.selectByPrimaryKey(-1);
    	logger.info("姓名："+langUser1.getName());
    	LangUser langUser2 = langUserMapper.selectByPrimaryKey(-1);
    	logger.info("姓名："+langUser2.getName());
    }

分析下console 其中有写日志我删除了为了方便大家阅读：  
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