构建树父类

public abstract class TreeBean<T extends TreeBean>{
    private String id;
    private String parentId;

    private List<T> children;
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getParentId() {
        return parentId;
    }

    public void setParentId(String parentId) {
        this.parentId = parentId;
    }

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

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

    public <T extends TreeBean> List<T> buildTree(List<T> result){
        List<T> treeList = new ArrayList<>();
        if(result==null||result.size()<=0) return treeList;
        List<String> ids = result.stream().map(t->t.getId()).collect(Collectors.toList());
        //从根节点建树
        for (T t : result) {
            //没有上级的时候，都可以当根结点
            if (t.getParentId() == null||!ids.contains(t.getParentId())) {
                recursiveBuild(t, result);
                treeList.add(t);
            }
        }
        return treeList;
    }

    /**递归当前节点构建
     *
     * @param parentNode
     * @param dataList
     */
    private  <T extends TreeBean> void recursiveBuild(T parentNode, List<T> dataList) {
        List<T> children = new ArrayList<>();
        for (T t : dataList) {
            if (t.getParentId() != null && t.getParentId().equals(parentNode.getId())) {
                recursiveBuild(t, dataList);
                children.add(t);
            }
        }
        parentNode.setChildren(children);
        afterBuildSingleTree(parentNode,children);
    }

    /**单个树枝构建完成后的处理，子类实现（父子要有其他联系操作，如子节点某个数据需要汇总到父节点上）
     * 
     * @param parent
     * @param children
     * @param <T>
     */
    abstract <T extends TreeBean> void afterBuildSingleTree(T parent,List<T> children);
}