mybatis缓存之一级缓存（一）

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

  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.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
  1. 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

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原文地址：https://www.cnblogs.com/zhenghengbin/p/13193999.html