1.Mybatis数据查询步骤

 2.在mappers映射器下创建文件（src/main/resources/mappers/goods.xml）

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="goods">


    <select id="selectAll" resultType="com.imooc.mybatis.entity.Goods" >
        select *
        from t_goods
        order by goods_id desc limit 10
    </select>
    
</mapper>

3.在mybatis-config.xml中对goods.xml声明

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

    <!-- 环境，可以配置多个，default：指定采用哪个环境 -->
    <environments default="dev">
        <!-- id：唯一标识 -->
        <environment id="dev">
            <!--采用JDBC进行事务的管理commit/rollback-->
            <transactionManager type="JDBC"/>
            <!-- 数据源，连接池类型的数据源 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url"
                          value="jdbc:mysql://localhost:3306/babytun?useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="197366"/>
            </dataSource>
        </environment>

    </environments>

    <!--声明mapper的配置文件-->
    <mappers>
        <mapper resource="mappers/goods.xml"/>
    </mappers>


</configuration>

4.测试语句

 /**
     * select查询语句执行
     *
     * @throws Exception
     */
    @Test
    public void testSelectAll() throws Exception
    {
        SqlSession session = null;
        try
        {
            session = MyBatisUtils.openSession();
            List<Goods> list = session.selectList("goods.selectAll");//goods.selectAll       命名空间.（SQL语句的ID）
            for (Goods g : list)
            {
                System.out.println(g.getTitle());
            }
        }
        catch (Exception e)
        {
            throw e;
        }
        finally
        {
            MyBatisUtils.closeSession(session);
        }
    }

5.在mybatis-config.xml中开启驼峰命名转换 

    <settings>
        <!-- goods_id ==> goodsId 驼峰命名转换 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>

6.CRUD标签（select标签）

select – 书写查询sql语句
select中的几个属性说明：
id属性：当前名称空间下的statement的唯一标识。必须。要求id和mapper接口中的方法的名字一致。
resultType：将结果集映射为java的对象类型。必须（和 resultMap 二选一）
parameterType：传入参数类型。可以省略