第二章分类，推荐，搜索，评价，购物车开发 - 1.5 分类实现 - 自定义 mapper 实现懒加载子分类展示 - 《Java 架构直通车》

在 foodie-dev-mapper 模块下的 com.imooc.mapper 包内创建 CategoryMapperCustom 接口

package com.imooc.mapper;
import com.imooc.pojo.vo.CategoryVO;
import java.util.List;
public interface CategoryMapperCustom {
    public List<CategoryVO> getSubCatList(Integer rootCatId);
}

在 foodie-dev-mapper 模块下的 resources 目录内创建 CategoryMapperCustom XML 文件
resultMap：映射到某一个具体的 pojo 类，

id：代表主键
column：对应 sql 中的列
property：对应实体类中的属性名
collection：用于定义关联的 list 集合类型的封装规则
- property：对应 pojo 类的属性
- ofType：此属性对应的类型是什么 ```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">

VO(View Object) 与 BO(Business Object) <br />BO 相当于业务型的，是从前端业务层封装过后的一些数据传入到后端，是发送一个请求过来的。如果是从内部传给前端，前端可以是 H5，可以是手机端，是展示在显示层的，显示层又称表现层（View Object）<br />在 foodie-dev-pojo 模块下新建 com.imooc.pojo.vo 包，创建 CategoryVO 类
```java
package com.imooc.pojo.vo;

import java.util.List;

/**
 * 二级分类 VO
 * Created by 92578 on 2020/8/22 19:57
 **/
public class CategoryVO {

    private Integer id;
    private String name;
    private String type;
    private Integer fatherId;

    // 三级分类 VO list
    private List<SubCategoryVO> subCatList;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Integer getFatherId() {
        return fatherId;
    }

    public void setFatherId(Integer fatherId) {
        this.fatherId = fatherId;
    }

    public List<SubCategoryVO> getSubCatList() {
        return subCatList;
    }

    public void setSubCatList(List<SubCategoryVO> subCatList) {
        this.subCatList = subCatList;
    }
}

在 foodie-dev-pojo 模块下的 com.imooc.pojo.vo 包内创建 SubCategoryVO 类

package com.imooc.pojo.vo;

/**
 * Created by 92578 on 2020/8/22 20:01
 **/
public class SubCategoryVO {

    private Integer subId;
    private String subName;
    private String subType;
    private Integer subFatherId;

    public Integer getSubId() {
        return subId;
    }

    public void setSubId(Integer subId) {
        this.subId = subId;
    }

    public String getSubName() {
        return subName;
    }

    public void setSubName(String subName) {
        this.subName = subName;
    }

    public String getSubType() {
        return subType;
    }

    public void setSubType(String subType) {
        this.subType = subType;
    }

    public Integer getSubFatherId() {
        return subFatherId;
    }

    public void setSubFatherId(Integer subFatherId) {
        this.subFatherId = subFatherId;
    }
}

在 foodie-dev-service 模块下的 CategoryService 接口添加 getSubCatlist 方法

package com.imooc.service;

import com.imooc.pojo.Category;
import com.imooc.pojo.vo.CategoryVO;

import java.util.List;

/**
 * Created by 92578 on 2020/8/22 16:17
 **/
public interface CategoryService {

    /**
     * 查询所有一级分类
     *
     * @return
     */
    public List<Category> queryAllRootLevelCat();

    /**
     * 根据一级分类 id 查询子分类信息
     *
     * @param rootCatId
     * @return
     */
    public List<CategoryVO> getSubCatlist(Integer rootCatId);
}

在 foodie-dev-service 模块下的 CategoryServiceImpl 类中实现 getSubCatlist 接口

package com.imooc.service.impl;

import com.imooc.mapper.CategoryMapper;
import com.imooc.mapper.CategoryMapperCustom;
import com.imooc.pojo.Category;
import com.imooc.pojo.vo.CategoryVO;
import com.imooc.service.CategoryService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
import tk.mybatis.mapper.entity.Example;

import java.util.List;

/**
 * Created by 92578 on 2020/8/22 16:18
 **/
@Service
public class CategoryServiceImpl implements CategoryService {

    @Autowired
    private CategoryMapper categoryMapper;

    @Autowired
    private CategoryMapperCustom categoryMapperCustom;

    /**
     * 查询所有一级分类
     *
     * @return
     */
    @Transactional(propagation = Propagation.SUPPORTS)
    @Override
    public List<Category> queryAllRootLevelCat() {
        Example example = new Example(Category.class);
        Example.Criteria criteria = example.createCriteria();
        criteria.andEqualTo("type", 1);

        List<Category> result = categoryMapper.selectByExample(example);

        return result;
    }

    /**
     * 根据一级分类 id 查询子分类信息
     *
     * @param rootCatId
     * @return
     */
    @Transactional(propagation = Propagation.SUPPORTS)
    @Override
    public List<CategoryVO> getSubCatlist(Integer rootCatId) {
        return categoryMapperCustom.getSubCatList(rootCatId);
    }
}

在 foodie-dev-api 模块下的 IndexController 类中添加 subCat 方法

package com.imooc.controller;

import com.imooc.enums.YseOrNo;
import com.imooc.pojo.Carousel;
import com.imooc.pojo.Category;
import com.imooc.pojo.vo.CategoryVO;
import com.imooc.service.CarouselService;
import com.imooc.service.CategoryService;
import com.imooc.utils.IMOOCJSONResult;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import io.swagger.annotations.ApiParam;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * Created by 92578 on 2020/8/22 16:30
 **/
@Api(value = "首页", tags = {"首页展示的相关接口"})
@RestController
@RequestMapping("index")
public class IndexController {

    @Autowired
    private CarouselService carouselService;

    @Autowired
    private CategoryService categoryService;

    @ApiOperation(value = "获取首页轮播图列表", notes = "获取首页轮播图列表", httpMethod = "GET")
    @GetMapping("/carousel")
    public IMOOCJSONResult carousel() {
        List<Carousel> list = carouselService.queryAll(YseOrNo.YES.type);

        return IMOOCJSONResult.ok(list);
    }

    @ApiOperation(value = "获取商品分类(一级分类)", notes = "获取商品分类(一级分类)", httpMethod = "GET")
    @GetMapping("/cats")
    public IMOOCJSONResult cats() {
        List<Category> list = categoryService.queryAllRootLevelCat();

        return IMOOCJSONResult.ok(list);
    }

    @ApiOperation(value = "获取商品子分类", notes = "获取商品子分类", httpMethod = "GET")
    @GetMapping("/subCat/{rootCatId}")
    public IMOOCJSONResult subCat(
            @ApiParam(name = "rootCatId", value = "一级分类 id", required = true)
            @PathVariable Integer rootCatId) {
        if (rootCatId == null) {
            return IMOOCJSONResult.errorMsg("分类不存在");
        }

        List<CategoryVO> list = categoryService.getSubCatlist(rootCatId);

        return IMOOCJSONResult.ok(list);
    }
}

启动项目，访问 http://localhost:8088/doc.html
找到“获取商品子分类”，点击“调试”，输入参数值“1”，点击“发送”

访问 http://localhost:8080/foodie-shop/index.html 子菜单已经可以展示出来