Deep Dive into MyBatis selectList() Execution Flow with MyBatis 3.5 and Spring Boot 2.3.3

This third article in a MyBatis source‑code series focuses on the selectList() method, assuming MyBatis 3.5 and Spring Boot 2.3.3 as the runtime environment.

The mapper interface is defined as List<UserInfo> selectList(@Param("userIds") List<String> userIds) , with a corresponding XML mapper that enables second‑level cache, declares a select statement, and uses a <foreach> to build the IN clause.

List<UserInfo> selectList(@Param("userIds") List<String> userIds);

<mapper namespace="cn.cb.demo.dao.UserMapper">
    <!--开启二级缓存-->
    <cache/>
    <select id="selectList" resultType="cn.cb.demo.domain.UserInfo">
        select * from user_info where status=1
        and user_id in
        <foreach collection="userIds" item="item" open="(" separator="," close=")">
            #{item}
        </foreach>
    </select>
</mapper>

A simple JUnit test calls the mapper with two user IDs and prints the returned list.

@Test
void contextLoads() {
    List<UserInfo> userInfos = userMapper.selectList(Arrays.asList("192", "198"));
    System.out.println(userInfos);
}

During debugging, Spring Boot injects SqlSessionTemplate , which forwards the call to DefaultSqlSession.selectList . The actual execution then passes through CachingExecutor.query , which first checks the second‑level cache, then delegates to BaseExecutor.query (first‑level cache), and finally to SimpleExecutor.doQuery for a database round‑trip.

The query method ultimately invokes prepareStatement(handler, ms.getStatementLog()) , bringing into play ParameterHandler and TypeHandler to set JDBC parameters. The DefaultParameterHandler.setParameters method iterates over all parameters, uses the appropriate TypeHandler to convert each value, and calls TypeHandler.setParameter .

After parameters are set, PreparedStatementHandler.query executes the SQL via JDBC and hands the ResultSet to DefaultResultSetHandler.handleResultSets . This handler obtains the result map, iterates over rows, applies TypeHandler.getResult for type conversion, and assembles the final list of UserInfo objects.

In summary, a selectList call follows the chain: SqlSessionTemplate → DefaultSqlSession → CachingExecutor → BaseExecutor → SimpleExecutor → ParameterHandler → PreparedStatementHandler → DefaultResultSetHandler , with caching, parameter preparation, and result mapping all orchestrated by MyBatis’s six core components.