递归构建下拉树

public List buildMenuTreeSelect(List menus) {
    List menuTrees = new ArrayList<>();
    List tempList = menus.stream().map(PrivilegeDTO::getId).collect(Collectors.toList());
    for (PrivilegeDTO menu : menus) {
        // 如果是顶级节点, 遍历该父节点的所有子节点
        if (!tempList.contains(menu.getParentId())) {
            recursionFn(menus, menu);
            menuTrees.add(menu);
        }
    }
    if (menuTrees.isEmpty()) {
        menuTrees = menus;
    }
    return menuTrees.stream().map(TreeSelect::new).collect(Collectors.toList());
}

/**
 * 递归列表,风暴大脑
 *
 * @param list       分类表
 * @param child      子节点
 */
private void recursionFn(List list, PrivilegeDTO child) {
    // 得到子节点列表
    List childList = getChildList(list, child);
    child.setChildren(childList);
    for (PrivilegeDTO p : childList) {
        //判断是否有子节点
        if (!getChildList(list, p).isEmpty()) {
            recursionFn(list, p);
        }
    }
}

/**
 * 得到子节点列表
 */
private List getChildList(List list, PrivilegeDTO child) {
    List tlist = new ArrayList<>();
    for (PrivilegeDTO privilegeDTO : list) {
        if (Objects.equals(privilegeDTO.getParentId(), child.getId())) {
            tlist.add(privilegeDTO);
        }
    }
    return tlist;
}

附实体treeSelect结构

public class TreeSelect implements Serializable {
    private static final long serialVersionUID = 1L;

    @ApiModelProperty("id")
    private Integer id;

    @ApiModelProperty("权限名称")
    private String name;

    @ApiModelProperty("子权限列表")

    //此注解可以使空值时此属性不返回于前端
    @JsonInclude(JsonInclude.Include.NON_EMPTY)
    private List children;

    public TreeSelect(PrivilegeDTO menu)
    {
        this.id = menu.getId();
        this.name = menu.getName();
        this.children = menu.getChildren().stream().map(TreeSelect::new).collect(Collectors.toList());
    }
}