list转化成tree

/**
 * 栏目列表转成树结构
 *
 * @param list
 * @return
 */
private static List<SysDict> listToTree(List<SysDict> list,Long id) {
    if (list == null || list.isEmpty()) {
        return list;
    }
    Map<Long, SysDict> sysDictMap = list.stream()
            .collect(Collectors.toMap(SysDict::getId, Function.identity()));
    // 树的顶层栏目
    SysDict root= new SysDict();
    sysDictMap.put(id, root);
    list.forEach(sysDict -> {
        Long pid = sysDict.getPid();
        SysDict parent = sysDictMap.get(pid);
        if (parent == null) {
            log.error("上层栏目分类不存在： {}", JSONUtil.toJsonStr(sysDict));
            return;
        }
        List<SysDict> children = parent.getChildren();
        // 初始化子层级
        if (children == null) {
            children = new ArrayList<>();
            parent.setChildren(children);
        }
        children.add(sysDict);
    });
    return root.getChildren();
}

list转化成tree

原文：https://www.cnblogs.com/tank073/p/14304582.html