对于mybatis框架。仿佛工作中一直是在copy着使用。对于mybatis缓存。并没有一个准确的认知。趁着假期。学习下mybatis的缓存。这篇主要学习mybatis的一级缓存。
为什么使用缓存
其实，大家工作久了，就知道很多瓶颈就是在数据库上。
初识mybatis一级缓存
当然我们还是通过代码来认识下mybatis的一级缓存
代码演示
详细代码见github，这里只展示重要的代码片段
- tempMapper.xml
<select id="getById" resultType="entity.TempEntity">
select * from temp where id = #{id}
</select>
- TempTest
public class TempTest {
Logger logger = Logger.getLogger(this.getClass());
@Test
public void test() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.TempDao.getById", 1);
logger.info(tempEntity1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.TempDao.getById", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}
}
3.运行结果
2020-06-26 08:57:37,453 DEBUG [dao.TempDao.getById] - ==> Preparing: select * from temp where id = ?
2020-06-26 08:57:37,513 DEBUG [dao.TempDao.getById] - ==> Parameters: 1(Integer)
2020-06-26 08:57:37,538 DEBUG [dao.TempDao.getById] - <== Total: 1
2020-06-26 08:57:37,538 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 08:57:37,538 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 08:57:37,538 INFO [TempTest] - true
- 总结
4.1 从上面的结果，我们可以看到,第二次查询的时候，就直接没有查询数据库，并且返回的是同一个对象。证明第二次走的就是缓存。
4.2 一级缓存是默认开启的。我们并没有在代码中配置任何关于缓存的配置
4.3 代码回顾
mybatis一级缓存命中原则
mybatis是怎么样判断某两次查询是完全相同的查询？
1.statementId
1.1 mapper.xml
<select id="getById1" resultType="entity.TempEntity">
select * from temp where id = #{id}
</select>
<select id="getById2" resultType="entity.TempEntity">
select * from temp where id = #{id}
</select>
1.2 test
@Test
public void test() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp2Dao.getById1", 1);
logger.info(tempEntity1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp2Dao.getById2", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}
1.3 结果
2020-06-26 09:19:09,926 DEBUG [dao.Temp2Dao.getById1] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:19:09,957 DEBUG [dao.Temp2Dao.getById1] - ==> Parameters: 1(Integer)
2020-06-26 09:19:09,969 DEBUG [dao.Temp2Dao.getById1] - <== Total: 1
2020-06-26 09:19:09,969 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 09:19:09,969 DEBUG [dao.Temp2Dao.getById2] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:19:09,970 DEBUG [dao.Temp2Dao.getById2] - ==> Parameters: 1(Integer)
2020-06-26 09:19:09,970 DEBUG [dao.Temp2Dao.getById2] - <== Total: 1
2020-06-26 09:19:09,971 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
1.4 总结
要求查询的statementId必须完全相同，否则无法命中缓存，即时两个查询语句、参数完全相同
2.查询参数
我们用不同的参数查询，一个传1 一个传2
2.1 test
@Test
public void testParam() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp2Dao.getById1", 1);
logger.info(tempEntity1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp2Dao.getById1", 2);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}
2.2 结果
2020-06-26 09:24:33,107 DEBUG [dao.Temp2Dao.getById1] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:24:33,148 DEBUG [dao.Temp2Dao.getById1] - ==> Parameters: 1(Integer)
2020-06-26 09:24:33,162 DEBUG [dao.Temp2Dao.getById1] - <== Total: 1
2020-06-26 09:24:33,162 INFO [TempTest] - TempEntity{id=1, value1='11111', value2='aaaaa'}
2020-06-26 09:24:33,162 DEBUG [dao.Temp2Dao.getById1] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:24:33,163 DEBUG [dao.Temp2Dao.getById1] - ==> Parameters: 2(Integer)
2020-06-26 09:24:33,164 DEBUG [dao.Temp2Dao.getById1] - <== Total: 1
2020-06-26 09:24:33,164 INFO [TempTest] - TempEntity{id=2, value1='22222', value2='bbbb'}
2020-06-26 09:24:33,164 INFO [TempTest] - false
2.3 总结
要求传递给sql的传递参数相同，否则不会命中缓存
3.分页参数
3.1 传不同的分页参数
@Test
public void testPage() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
RowBounds rowBounds1 = new RowBounds(0,1);
List<TempEntity> tempEntity1 = sqlSession.selectList("dao.Temp2Dao.getList", null,rowBounds1);
logger.info(tempEntity1);
RowBounds rowBounds2 = new RowBounds(0,2);
List<TempEntity> tempEntity2 = sqlSession.selectList("dao.Temp2Dao.getList",null, rowBounds2);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}
3.2 结果
2020-06-26 10:10:33,060 DEBUG [dao.Temp2Dao.getList] - ==> Preparing: select * from temp where 1=1
2020-06-26 10:10:33,101 DEBUG [dao.Temp2Dao.getList] - ==> Parameters:
2020-06-26 10:10:33,116 INFO [TempTest] - [TempEntity{id=1, value1='11111', value2='aaaaa'}]
2020-06-26 10:10:33,116 DEBUG [dao.Temp2Dao.getList] - ==> Preparing: select * from temp where 1=1
2020-06-26 10:10:33,116 DEBUG [dao.Temp2Dao.getList] - ==> Parameters:
2020-06-26 10:10:33,118 INFO [TempTest] - [TempEntity{id=1, value1='11111', value2='aaaaa'}, TempEntity{id=2, value1='22222', value2='bbbb'}]
2020-06-26 10:10:33,118 INFO [TempTest] - false
3.3 总结
要求分页参数必须相同，否则无法命中缓存。缓存的粒度是整个分页查询结果，而不是结果中的每个对象
4. sql语句
4.1 mapper文件
<select id="getById" resultType="entity.TempEntity">
select * from temp
<where>
<if test="type ==1">
id = #{id}
</if>
<if test="type ==2">
1=1 and id = #{id}
</if>
</where>
</select>
这个就不测试了。
4.2 总结
要求传递给jdbc的sql 必须完全相同。就算是1=1 不起作用 也不行
5.环境
这里的环境指的的是<environment id="dev"> 和 <environment id="test"> 也是会影响的
<environments default="dev">
<environment id="dev">
<!--指定事务管理的类型，这里简单使用Java的JDBC的提交和回滚设置-->
<transactionManager type="JDBC"></transactionManager>
<!--dataSource 指连接源配置，POOLED是JDBC连接对象的数据源连接池的实现-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"></property>
<property name="url" value="jdbc:mysql://127.0.0.1:3306/test"></property>
<property name="username" value="root"></property>
<property name="password" value="root"></property>
</dataSource>
</environment>
<environment id="test">
<!--指定事务管理的类型，这里简单使用Java的JDBC的提交和回滚设置-->
<transactionManager type="JDBC"></transactionManager>
<!--dataSource 指连接源配置，POOLED是JDBC连接对象的数据源连接池的实现-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"></property>
<property name="url" value="jdbc:mysql://127.0.0.1:3306/test"></property>
<property name="username" value="root"></property>
<property name="password" value="root"></property>
</dataSource>
</environment>
</environments>
总结
