list转树形结构

1、两层for循环

public static List<NodeVO> streamToTree(List<NodeVO> treeList, String parentId) {
    List<NodeVO> result = new ArrayList<>();
    for(int i = 0; i < treeList.length; i++){
        if(treeList[j].getPid() == parentId){
            result.add(treeList[i]);
        }
        List<NodeVO> childList = new ArrayList<>();
        for(int j = 0; j < treeList.length; j++){   
            if( treeList[j].getPid() == treeList[i].getId()){
                childList.add(treeList[j]);
            }
        } 
        treeList[i].setChildren(childList);
    }
    return result;
}

2、stream流

public static List<NodeVO> streamToTree(List<NodeVO> treeList, String parentId) {
    List<NodeVO> list = treeList.stream()
            // 过滤父节点
            .filter(parent -> parent.getPid().equals(parentId))
            // 把父节点children递归赋值成为子节点
            .map(child -> {
                child.setChildren(streamToTree(treeList,child.getId()));
                return child;
            }).collect(Collectors.toList());
    return list;
}