使用java+mybaits技术实现 ，订单表和商品表的一对多查询 ，并打印，用户表和订单表的一对一查询，并打印

假设订单表的表名为 `order`，商品表的表名为 `product`，用户表的表名为 `user`，并且它们的关联字段如下：

- `order` 表的 `product_id` 字段与 `product` 表的 `id` 字段关联
- `order` 表的 `user_id` 字段与 `user` 表的 `id` 字段关联

一对多查询订单表和商品表的代码如下：

public class Order {
    private int id;
    private int user_id;
    private int product_id;
    private int quantity;
    // getter and setter
}

public class Product {
    private int id;
    private String name;
    private double price;
    // getter and setter
}

public class OrderMapper {
    public List<Order> selectOrdersWithProduct() {
        try (SqlSession session = sqlSessionFactory.openSession()) {
            return session.selectList("selectOrdersWithProduct");
        }
    }
}

对应的 MyBatis XML 配置文件如下：

<mapper namespace="com.example.mapper.OrderMapper">
    <select id="selectOrdersWithProduct" resultType="com.example.model.Order">
        SELECT o.*, p.name, p.price
        FROM order o
        LEFT JOIN product p ON o.product_id = p.id
    </select>
</mapper>

一对一查询用户表和订单表的代码如下：

public class User {
    private int id;
    private String name;
    private String email;
    private Order order;
    // getter and setter
}

public class Order {
    private int id;
    private int user_id;
    private int product_id;
    private int quantity;
    // getter and setter
}

public class UserMapper {
    public User selectUserWithOrder(int user_id) {
        try (SqlSession session = sqlSessionFactory.openSession()) {
            return session.selectOne("selectUserWithOrder", user_id);
        }
    }
}

对应的 MyBatis XML 配置文件如下：

<mapper namespace="com.example.mapper.UserMapper">
    <select id="selectUserWithOrder" resultMap="userWithOrderResultMap">
        SELECT u.*, o.id as order_id, o.product_id, o.quantity
        FROM user u
        LEFT JOIN order o ON u.id = o.user_id
        WHERE u.id = #{id}
    </select>
    
    <resultMap id="userWithOrderResultMap" type="com.example.model.User">
        <id property="id" column="id" />
        <result property="name" column="name" />
        <result property="email" column="email" />
        <association property="order" javaType="com.example.model.Order">
            <id property="id" column="order_id" />
            <result property="product_id" column="product_id" />
            <result property="quantity" column="quantity" />
        </association>
    </resultMap>
</mapper>

以上代码仅供参考，具体实现需要根据实际业务进行修改。