主题
分享记录一下MyBatis的一级缓存相关的学习.
Demo
1 public static void firstLevelCache() { 2 init("mybatis-config.xml"); 3 4 SqlSession session = sqlSessionFactory.openSession(); 5 6 UserMapper mapper = session.getMapper(UserMapper.class); 7 User u = mapper.selectByPrimaryKey(1); 8 System.out.println(u); 9 10 User u2 = mapper.selectByPrimaryKey(1); 11 System.out.println(u2); 12 session.close(); 13 14 System.out.println("==============session2=============="); 15 16 SqlSession session2 = sqlSessionFactory.openSession(); 17 UserMapper mapper2 = session2.getMapper(UserMapper.class); 18 User u3 = mapper2.selectByPrimaryKey(1); 19 System.out.println(u3); 20 session2.close(); 21 22 }
从1个Demo来学习.
上面这段代码首先通过session获取了mapper然后执行了2次同样的查询,查询用户ID为1的数据, 然后打印=======session2======,然后新开了一个session2. 然后获取了第二个mapper并执行了相同的查询.
输出结果:
2018-09-29 19:06:26,813 DEBUG [main] logging.LogFactory : Logging initialized using 'class org.apache.ibatis.logging.slf4j.Slf4jImpl' adapter. 2018-09-29 19:06:26,961 DEBUG [main] pooled.PooledDataSource : PooledDataSource forcefully closed/removed all connections. 2018-09-29 19:06:26,962 DEBUG [main] pooled.PooledDataSource : PooledDataSource forcefully closed/removed all connections. 2018-09-29 19:06:26,962 DEBUG [main] pooled.PooledDataSource : PooledDataSource forcefully closed/removed all connections. 2018-09-29 19:06:26,962 DEBUG [main] pooled.PooledDataSource : PooledDataSource forcefully closed/removed all connections. 2018-09-29 19:06:27,102 DEBUG [main] jdbc.JdbcTransaction : Opening JDBC Connection Sat Sep 29 19:06:27 CST 2018 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification. 2018-09-29 19:06:28,095 DEBUG [main] pooled.PooledDataSource : Created connection 1682463303. 2018-09-29 19:06:28,095 DEBUG [main] jdbc.JdbcTransaction : Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@64485a47] 2018-09-29 19:06:28,108 DEBUG [main] UserMapper.selectByPrimaryKey : ==> Preparing: select id, user_id, user_name, real_name, email, creator_uid, modifier_uid, created_at, updated_at, del from user where id = ? 2018-09-29 19:06:28,145 DEBUG [main] UserMapper.selectByPrimaryKey : ==> Parameters: 1(Integer) 2018-09-29 19:06:28,172 DEBUG [main] UserMapper.selectByPrimaryKey : <== Total: 1 User{id=1, userId=1, userName='test', realName='realName', email='[email protected]', creatorUid=1, modifierUid=1, createdAt=Mon Sep 24 10:10:43 CST 2018, updatedAt=Mon Sep 24 10:10:46 CST 2018, del=false} User{id=1, userId=1, userName='test', realName='realName', email='[email protected]', creatorUid=1, modifierUid=1, createdAt=Mon Sep 24 10:10:43 CST 2018, updatedAt=Mon Sep 24 10:10:46 CST 2018, del=false} 2018-09-29 19:06:28,172 DEBUG [main] jdbc.JdbcTransaction : Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@64485a47] 2018-09-29 19:06:28,183 DEBUG [main] jdbc.JdbcTransaction : Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@64485a47] 2018-09-29 19:06:28,183 DEBUG [main] pooled.PooledDataSource : Returned connection 1682463303 to pool. ==============session2============== 2018-09-29 19:06:28,183 DEBUG [main] jdbc.JdbcTransaction : Opening JDBC Connection 2018-09-29 19:06:28,183 DEBUG [main] pooled.PooledDataSource : Checked out connection 1682463303 from pool. 2018-09-29 19:06:28,183 DEBUG [main] jdbc.JdbcTransaction : Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@64485a47] 2018-09-29 19:06:28,193 DEBUG [main] UserMapper.selectByPrimaryKey : ==> Preparing: select id, user_id, user_name, real_name, email, creator_uid, modifier_uid, created_at, updated_at, del from user where id = ? 2018-09-29 19:06:28,194 DEBUG [main] UserMapper.selectByPrimaryKey : ==> Parameters: 1(Integer) 2018-09-29 19:06:28,210 DEBUG [main] UserMapper.selectByPrimaryKey : <== Total: 1 User{id=1, userId=1, userName='test', realName='realName', email='[email protected]', creatorUid=1, modifierUid=1, createdAt=Mon Sep 24 10:10:43 CST 2018, updatedAt=Mon Sep 24 10:10:46 CST 2018, del=false} 2018-09-29 19:06:28,210 DEBUG [main] jdbc.JdbcTransaction : Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@64485a47] 2018-09-29 19:06:28,221 DEBUG [main] jdbc.JdbcTransaction : Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@64485a47] 2018-09-29 19:06:28,221 DEBUG [main] pooled.PooledDataSource : Returned connection 1682463303 to pool.
从输出中我们可以看到,红色部分是执行的SQL,总共执行了3次查询,但是SQL执行运行了2次.而使用第2个session查询的时候仍然会触发SQL的执行.
从中我们可以得到结论:
一级缓存是发生在同一个SqlSession中的, 1个sqlSession 多次执行相同的SQL查询会有缓存
如何缓存
然后我们来学习下跟着断点看看MyBatis是如何缓存执行结果的,都涉及到哪些比较重要的类.