java8 创建树结构的数据

private List<TreeNode> createTree(Integer pid, Map<Integer, List<SysPermission>> map){
    return Optional.ofNullable(map.get(pid)).orElseGet(()->new ArrayList<SysPermission>()).stream().filter(x->x.getParentId() == pid).sorted((x,y)->{return x.getSortNo().compareTo(y.getSortNo());}).map(x->{
        return new TreeNode(x.getRecId(), x.getParentId(), x.getPermissionName(), x.getIcon(), createTree(x.getRecId(), map));
    }).collect(Collectors.toList());
}

private List<TreeNode> getTree(boolean onlyModule){
    EntityWrapper<SysPermission> entityWrapper = new EntityWrapper<>();
    entityWrapper.where("data_status>0");
    if (onlyModule){
        entityWrapper.eq("permission_type", PermissionType.MODULE.getValue());
    }
    entityWrapper.orderBy("sort_no");
    List<SysPermission> list = selectList(entityWrapper);
    return createTree(0, list.stream().collect(groupingBy(SysPermission::getParentId)));
}

TreeNode的定义：

public class TreeNode {
    private static final long serialVersionUID = 1L;

    private Integer recId;
    private Integer pid;
    private String nodeName;
    private String icon;
    private List<TreeNode> children;

    public TreeNode(Integer recId, Integer pid, String nodeName, String icon) {
        this.recId = recId;
        this.pid = pid;
        this.nodeName = nodeName;
        this.icon = icon;
        this.children = new ArrayList<TreeNode>();
    }

    public TreeNode(Integer recId, Integer pid, String nodeName, String icon, List<TreeNode> children) {
        this.recId = recId;
        this.pid = pid;
        this.nodeName = nodeName;
        this.icon = icon;
        this.children = children;
    }

    public Integer getRecId() {
        return recId;
    }

    public void setRecId(Integer recId) {
        this.recId = recId;
    }

    public Integer getPid() {
        return pid;
    }

    public void setPid(Integer pid) {
        this.pid = pid;
    }

    public String getNodeName() {
        return nodeName;
    }

    public void setNodeName(String nodeName) {
        this.nodeName = nodeName;
    }

    public String getIcon() {
        return icon;
    }

    public void setIcon(String icon) {
        this.icon = icon;
    }

    public List<TreeNode> getChildren() {
        return children;
    }

    public void setChildren(List<TreeNode> children) {
        this.children = children;
    }
}