java List 构建树状结构

一、SQL

SELECT
    categoryCode AS 'id',
    categoryName AS 'label',
    parentCode AS 'parentId' 
FROM
    a

二、JAVA代码

/**
     * 创建树形结构菜单列表
     *
     * @param menus
     * @return
     */
    public static List<PlaCategoryTreeDto> createTreeMenus(List<PlaCategoryTreeDto> menus) {
        List<PlaCategoryTreeDto> treeMenus = null;
        //判断非空
        if (null != menus && !menus.isEmpty()) {
            // 创建根节点
            PlaCategoryTreeDto root = new PlaCategoryTreeDto();
            root.setLabel("菜单根目录");

            // 组装Map数据
            Map<String, PlaCategoryTreeDto> dataMap = new HashMap<>();
            for (PlaCategoryTreeDto menu : menus) {
                dataMap.put(menu.id, menu);
            }

            // 组装树形结构
            Set<Map.Entry<String, PlaCategoryTreeDto>> entrySet = dataMap.entrySet();
            //foreach遍历
            for (Map.Entry<String, PlaCategoryTreeDto> entry : entrySet) {
                PlaCategoryTreeDto menu = entry.getValue();
                //判断是父节点还是子节点
                if (StringUtil.isEmpty(menu.getParentId()) || "1".equals(menu.getParentId())) {
                    //父节点
                    if (root.getChildren() == null) {
                        //子节点为空
                        List<PlaCategoryTreeDto> tempList = new ArrayList<>();
                        tempList.add(menu);
                        root.setChildren(tempList);
                    } else {
                        //子节点不为空
                        root.getChildren().add(menu);
                    }
                } else {
                    //子节点
                    PlaCategoryTreeDto parentMenu = dataMap.get(menu.getParentId());
                    //如果为null说明父级节点不显示，则对应的子级节点也不显示
                    if (parentMenu != null) {
                        if (parentMenu.getChildren() == null) {
                            //子节点为空
                            List<PlaCategoryTreeDto> tempList = new ArrayList<>();
                            tempList.add(menu);
                            dataMap.get(menu.getParentId()).setChildren(tempList);
                        } else {
                            //子节点不为空
                            dataMap.get(menu.getParentId()).getChildren().add(menu);
                        }
                    }
                }
            }

            treeMenus = root.getChildren();
        }
        return treeMenus;
    }

三、JSON

{
    "body": {
        "data": [
            {
                "id": "0217fb7d-03ef-4a91-ac12-30720e170f5d",
                "label": "数码产品",
                "parentId": "1",
                "children": [
                    {
                        "id": "fc5e438f-cd13-4d55-93aa-7ce7ab9777f6",
                        "label": "相机",
                        "parentId": "0217fb7d-03ef-4a91-ac12-30720e170f5d",
                        "children": null
                    }
                ]
            },
            {
                "id": "b9cc292d-02df-41d9-8f4d-f376c8b9613c",
                "label": "服装",
                "parentId": "1",
                "children": [
                    {
                        "id": "3129f97b-4ffe-4740-8654-7b7a92468598",
                        "label": "男装",
                        "parentId": "b9cc292d-02df-41d9-8f4d-f376c8b9613c",
                        "children": null
                    },
                    {
                        "id": "b2db9dd3-9a93-453c-a4d8-9d376875cda4",
                        "label": "女装",
                        "parentId": "b9cc292d-02df-41d9-8f4d-f376c8b9613c",
                        "children": null
                    },
                    {
                        "id": "ec83d829-5f8e-47fb-a6eb-4841845d68e8",
                        "label": "童装",
                        "parentId": "b9cc292d-02df-41d9-8f4d-f376c8b9613c",
                        "children": null
                    }
                ]
            }
        ]
    }
}