對於mybatis框架。仿佛工作中一直是在copy着使用。對於mybatis緩存。並沒有一個准確的認知。趁着假期。學習下mybatis的緩存。這篇主要學習mybatis的一級緩存。
為什么使用緩存
其實，大家工作久了，就知道很多瓶頸就是在數據庫上。
初識mybatis一級緩存
當然我們還是通過代碼來認識下mybatis的一級緩存
代碼演示
詳細代碼見github，這里只展示重要的代碼片段
- 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.運行結果
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
- 總結
4.1 從上面的結果，我們可以看到,第二次查詢的時候，就直接沒有查詢數據庫，並且返回的是同一個對象。證明第二次走的就是緩存。
4.2 一級緩存是默認開啟的。我們並沒有在代碼中配置任何關於緩存的配置
4.3 代碼回顧
mybatis一級緩存命中原則
mybatis是怎么樣判斷某兩次查詢是完全相同的查詢？
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 結果
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 總結
要求查詢的statementId必須完全相同，否則無法命中緩存，即時兩個查詢語句、參數完全相同
2.查詢參數
我們用不同的參數查詢，一個傳1 一個傳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 結果
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 總結
要求傳遞給sql的傳遞參數相同，否則不會命中緩存
3.分頁參數
3.1 傳不同的分頁參數
@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 結果
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 總結
要求分頁參數必須相同，否則無法命中緩存。緩存的粒度是整個分頁查詢結果，而不是結果中的每個對象
4. sql語句
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>
這個就不測試了。
4.2 總結
要求傳遞給jdbc的sql 必須完全相同。就算是1=1 不起作用 也不行
5.環境
這里的環境指的的是<environment id="dev"> 和 <environment id="test"> 也是會影響的
<environments default="dev">
<environment id="dev">
<!--指定事務管理的類型，這里簡單使用Java的JDBC的提交和回滾設置-->
<transactionManager type="JDBC"></transactionManager>
<!--dataSource 指連接源配置，POOLED是JDBC連接對象的數據源連接池的實現-->
<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">
<!--指定事務管理的類型，這里簡單使用Java的JDBC的提交和回滾設置-->
<transactionManager type="JDBC"></transactionManager>
<!--dataSource 指連接源配置，POOLED是JDBC連接對象的數據源連接池的實現-->
<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>
總結
