mybatis快取之一級快取（一）

Kevin_zheng發表於2020-06-26
MyBatis快取

對於mybatis框架。彷彿工作中一直是在copy著使用。對於mybatis快取。並沒有一個準確的認知。趁著假期。學習下mybatis的快取。這篇主要學習mybatis的一級快取。

為什麼使用快取

其實，大家工作久了，就知道很多瓶頸就是在資料庫上。

初識mybatis一級快取

當然我們還是通過程式碼來認識下mybatis的一級快取

程式碼演示

詳細程式碼見github，這裡只展示重要的程式碼片段

  1. tempMapper.xml
    <select id="getById" resultType="entity.TempEntity">
       select * from  temp where id = #{id}
    </select>
  1. 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.執行結果

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
  1. 總結

4.1 從上面的結果，我們可以看到,第二次查詢的時候，就直接沒有查詢資料庫，並且返回的是同一個物件。證明第二次走的就是快取。
4.2 一級快取是預設開啟的。我們並沒有在程式碼中配置任何關於快取的配置
4.3 程式碼回顧

mybatis一級快取命中原則

mybatis是怎麼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，否則無法命中快取，即時兩個查詢語句、引數完全相同

2.查詢引數

我們用不同的引數查詢，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的傳遞引數相同，否則不會命中快取

3.分頁引數

3.1 傳不同的分頁引數

    @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

要求分頁引數必須相同，否則無法命中快取。快取的粒度是整個分頁查詢結果，而不是結果中的每個物件

4. sql語句

4.1 mapper檔案

    <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

這裡的環境指的的是<environment id="dev"> 和 <environment id="test"> 也是會影響的

    <environments default="dev">
        <environment id="dev">
            <!--指定事務管理的型別，這裡簡單使用Java的JDBC的提交和回滾設定-->
            <transactionManager type="JDBC"></transactionManager>
            <!--dataSource 指連線源配置，POOLED是JDBC連線物件的資料來源連線池的實現-->
            <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">
            <!--指定事務管理的型別，這裡簡單使用Java的JDBC的提交和回滾設定-->
            <transactionManager type="JDBC"></transactionManager>
            <!--dataSource 指連線源配置，POOLED是JDBC連線物件的資料來源連線池的實現-->
            <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

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