Java分级列表 对象传值一直为空

在写商品分类多级列表时，
问题出在Controller层的第12，13，14行
12行我打印对象是存在的，但是13行赋值时一直为空

public Map<String,Object> findAll() {
        Map<String,Object> map = new HashMap<>();
        try {
            Map<String,Object> map1 = new HashMap<>();
            List<Category> categorys =categoryService.findAll();
            //存放所有一级目录
            List<CategoryTwo> categoryTwos = new ArrayList();
            
            //找出父级目录
            for(Category category : categorys){
                    if(category.getCat_pid() == 0){
                        System.out.println(category);
                        CategoryTwo categoryTwo = new CategoryTwo(category);
                        categoryTwos.add(categoryTwo);//存入一级目录集合中
                        System.out.println(categoryTwos);
                    }
            }
            map1.put("msg","获取成功");
            map1.put("status",200);
            map.put("meta",map1);
        }catch (Exception e){
            e.printStackTrace();
        }

        return map;
    }

运行结果

父级实体对象

public class Category {
    private Integer cat_id;
    private String cat_name;
    private Integer cat_pid;
    private Integer cat_level;
    private String cat_icon;
    public List children;
}

二级实体对象

public class CategoryTwo extends Category{
    private List<CategoryTwo> categorieTwos;
    public CategoryTwo(Category category){
        super(category.getCat_id(),category.getCat_name(),category.getCat_pid(),
                category.getCat_level(),category.getCat_icon(),category.getChildren());
    }
}

数据库

你貌似并没有把 categoryTwos 赋值进去CategoryTwo ？

二级实体对象里面的categorieTwos 没有看到有赋值的地方。

复制你的代码，看看有没有不一样的地方

import java.util.List;

public class Category {

    private Integer cat_id;
    private String cat_name;
    private Integer cat_pid;
    private Integer cat_level;
    private String cat_icon;
    public List children;
    
    public Category(Integer cat_id, String cat_name, Integer cat_pid, Integer cat_level, String cat_icon,
            List children) {
        this.cat_id = cat_id;
        this.cat_name = cat_name;
        this.cat_pid = cat_pid;
        this.cat_level = cat_level;
        this.cat_icon = cat_icon;
        this.children = children;
    }
    public Integer getCat_id() {
        return cat_id;
    }
    public void setCat_id(Integer cat_id) {
        this.cat_id = cat_id;
    }
    public String getCat_name() {
        return cat_name;
    }
    public void setCat_name(String cat_name) {
        this.cat_name = cat_name;
    }
    public Integer getCat_pid() {
        return cat_pid;
    }
    public void setCat_pid(Integer cat_pid) {
        this.cat_pid = cat_pid;
    }
    public Integer getCat_level() {
        return cat_level;
    }
    public void setCat_level(Integer cat_level) {
        this.cat_level = cat_level;
    }
    public String getCat_icon() {
        return cat_icon;
    }
    public void setCat_icon(String cat_icon) {
        this.cat_icon = cat_icon;
    }
    public List getChildren() {
        return children;
    }
    public void setChildren(List children) {
        this.children = children;
    }
    @Override
    public String toString() {
        return "Category [cat_id=" + cat_id + ", cat_name=" + cat_name + ", cat_pid=" + cat_pid + ", cat_level="
                + cat_level + ", cat_icon=" + cat_icon + ", children=" + children + "]";
    }

}

import java.util.List;

public class CategoryTwo extends Category {
    private List<CategoryTwo> categorieTwos;

    public CategoryTwo(Category category) {
        super(category.getCat_id(), category.getCat_name(), category.getCat_pid(), category.getCat_level(),
                category.getCat_icon(), category.getChildren());
    }
}