Mybatis使用xml配置方式启动

前面做了零xml的mybatis配置启动，但是官方给出的意见是：

…映射器类是 Java 类，它们包含 SQL 映射注解从而避免依赖 XML 文件。不过，由于 Java 注解的一些限制以及某些 MyBatis 映射的复杂性，要使用大多数高级映射（比如：嵌套联合映射），仍然需要使用 XML 配置.

单击main，command+n，

点击下面的resources
在config层新建一个MybatisConfigXml类

public class MybatisConfigXml {
    
    
    private static SqlSessionFactory sqlSessionFactory;

    private MybatisConfigXml() {
    
    
    }

    static {
    
    
        try {
    
    
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis-config.xml"));
        } catch (IOException e) {
    
    
            e.printStackTrace();
        }
    }

    public static SqlSessionFactory getSqlSessionFactory() {
    
    
        return sqlSessionFactory;
    }

}

dao下新建映射器UserMapper

public interface UserMapper {
    /**
     *
     * @param id
     * @return
     */
    String selectUserName(int id);
}

在resources下新建mapper，新建同名映射文件UserMapper.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="org.example.dao.UserMapper">
    <select id="selectUserName" parameterType="int" resultType="String">
        select name from users where id=#{id};
    </select>
</mapper>

在resources下新建配置文件mybatis-config.xml，注意这里使用了properties标签，单独保存数据库链接信息，这样方便管理。

<?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>
    <properties resource="jdbc.properties">
<!--        <property name="username" value="root"/>-->
<!--        <property name="password" value="root"/>-->
    </properties>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

jdbc.properties

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/Jan_test_learn
username=root
password=

主类

public class App {
    
    
    public static void main(String[] args) {
    
    
        SqlSessionFactory sqlSessionFactory = MybatisConfigXml.getSqlSessionFactory();
        /*创建SqlSession，线程不安全的*/
        SqlSession sqlSession = sqlSessionFactory.openSession();
        /*获取mapper实例*/
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        String name = userMapper.selectUserName(1);
        System.out.println(name);
        sqlSession.close();
    }
}

成功启动