JAVA构建树状结构

记一下自己在展示树状结构时候的几个写法，一个是确定有几个层级的，用于只有两三个层级的树状结构，写法简单一点。还有就是不确定有几个层级，也可能1个，也可能4个或者更多。

先说一下确定有几个层级的写法

这是需要用的树状结构实体类

	//父级菜单id
    private Long id;
    //父级菜单名称
    private String label;
	//子菜单信息
    private List children;

    public TreeSelect() {
    }

    public TreeSelect(XXX  xxx) {
        this.id = xxx.getId();
        this.label = xxx.gexxname();
        this.professorName = xxx.getxxxame();
        this.children = xxx.getChildren().stream().map(TreeSelect::new).collect(Collectors.toList());      
    }

明确几个层级的写法（这里是只有两级），做了两个foreach

//入参的list是查询出来的父级菜单的信息
public List treeSelectList(List indexInfoList) {
     List treeSelectList = new ArrayList<>();
     indexInfoList.stream().forEach(e -> {
     TreeSelect treeSelect = new TreeSelect();
     //设置大类信息
     if (e.getIndexPid() == 0) {
     treeSelect.setId(e.getId());
     treeSelect.setLabel(e.getIndexPname());
     List secondTree = new ArrayList<>();
     //根据id查询小类信息
     QueryWrapper queryWrapper = new QueryWrapper()
     .eq("id", e.getId());
     List indexInfos = indexInfoMapper.selectList(queryWrapper);
     //设置小类信息
     indexInfos.stream().forEach(indexInfo -> {
     TreeSelect secondTreeSelect = new TreeSelect();
     secondTreeSelect.setId(indexInfo.getId());
     secondTreeSelect.setLabel(indexInfo.getIndexPname());
     secondTree.add(secondTreeSelect);
     });
     //添加集合
     treeSelect.setChildren(secondTree);
     treeSelectList.add(treeSelect);
     }
     });
     return treeSelectList;
     }

下面是不确定几个层级，递归写法

方法类：

    
    public List treeSelectList(List indexInfoList) {
        List trees = buildIndexTree(indexInfoList);
        return trees.stream().map(TreeSelect::new).collect(Collectors.toList());
    }

    
    public List buildIndexTree(List indexInfoList) {
        List returnList = new ArrayList();
        List indexList = new ArrayList();
        //一级菜单设置信息
        for (IndexInfo indexInfo : indexInfoList) {
            indexList.add(indexInfo.getId());
        }
        for (Iterator iterator = indexInfoList.iterator(); iterator.hasNext(); ) {
            IndexInfo indexInfo =iterator.next();
            // 如果是顶级节点, 遍历该父节点的所有子节点
            if (!indexList.contains(indexInfo.getIndexPid())) {
                recursionFn(indexInfoList, indexInfo);
                returnList.add(indexInfo);
            }
        }
        if (returnList.isEmpty()) {
            returnList = indexInfoList;
        }
        return returnList;
    }

    
    private void recursionFn(List list, IndexInfo t) {
        // 得到子节点列表
        List childList = getChildList(list, t);
        t.setChildren(childList);
        for (IndexInfo tChild : childList) {
            if (hasChild(list, tChild)) {
                recursionFn(list, tChild);
            }
        }
    }

    
    private List getChildList(List list, IndexInfo t) {
        List tlist = new ArrayList();
        Iterator it = list.iterator();
        while (it.hasNext()) {
            IndexInfo n = it.next();
            if (StringUtils.isNotNull(n.getIndexPid()) && n.getIndexPid().longValue() == t.getId().longValue()) {
                tlist.add(n);
            }
        }
        return tlist;
    }

    
    private boolean hasChild(List list, IndexInfo t) {
        return getChildList(list, t).size() > 0 ? true : false;
    }

附上结果：

    "msg": "操作成功",
    "code": 200,
    "data": [
        {
            "id": 1,
            "label": "指标名称1"
            "children": [
                {
                    "id": 4,
                    "label": "指标名称1-1"
                    "children": [
                        {
                            "id": 10,
                            "label": "指标名称1-1-1"
                        },
                        {
                            "id": 11,
                            "label": "指标名称1-1-2"
                        }
                    ]
                },
                {
                    "id": 5,
                    "label": "指标名称1-2"
                }
            ]
        }
    ]
}