Java构造前端vue使用的树（或者使用Java构造常用的部门树等）

  Web项目开发中，由于前端框架的限制，很多时候需要将返回的数据加工后再返回给前端。最典型的就是返回一棵部门层级关系的树。下面即是一棵带有层级的文档标题树，和我们书籍的目录结构一样。

  在树的结构中，每一个节点都需要有一颗父级节点，即使是*节点，也需要给其父节点赋值。比如，在下面的带有父子关系的线性结构中，有些id的parentId是null的，此时就需要将parentId为null赋值为projectId。同时使用了fastjson作为辅助工具，具有一定的通用性。其数值如下：

"data": [
            {
                "id": "661661966154199040",
                "text": null,
                "parentId": null,//父级id为空，需要将其赋值为projectId
                "orderCount": 0,
                "projectId": "741917334711331456",
                "children": null//下级节点
            },
            {
                "id": "661662130646413312",
                "text": null,
                "parentId": null,
                "orderCount": 1,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "661662428978868224",
                "text": null,
                "parentId": null,
                "orderCount": 2,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "772919473459032064",
                "text": null,
                "parentId": "653294833572617088",
                "orderCount": 2,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "772917879430574080",
                "text": null,
                "parentId": "653294833572617088",
                "orderCount": 3,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "661661793088827392",
                "text": null,
                "parentId": null,
                "orderCount": 4,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "661661918448185344",
                "text": null,
                "parentId": null,
                "orderCount": 5,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "772919255229394944",
                "text": null,
                "parentId": null,
                "orderCount": 6,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "661661956607963136",
                "text": null,
                "parentId": null,
                "orderCount": 7,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "661661957128056832",
                "text": null,
                "parentId": null,
                "orderCount": 8,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "653294833572617088",
                "text": null,
                "parentId": null,
                "orderCount": 11,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "653370321808759680",
                "text": null,
                "parentId": null,
                "orderCount": 11,
                "projectId": "741917334711331456",
                "children": null
            },
            {
                "id": "653385876393532288",
                "text": null,
                "parentId": null,
                "orderCount": 11,
                "projectId": "741917334711331456",
                "children": null
            }
        ]

树的DTO结构如***意children:

public class TreeDTO {

    /** 儿子id **/
    private Long id;

    /** 附带文本 **/
    private String text;

    /** 父级id **/
    private Long parentId;

    /** 排序值 **/
    private Integer orderCount;

    /** 项目id **/
    private Long projectId;

    /** 孩子节点 **/
    private List<TreeDTO> children;

    /**
     * @return the text
     */
    public String getText() {
        return text;
    }

    /**
     * @param text
     */
    public void setText(String text) {
        this.text = text;
    }

    /**
     * @return the id
     */
    public Long getId() {
        return id;
    }

    /**
     * @param id
     */
    public void setId(Long id) {
        this.id = id;
    }

    /**
     * @return the parentId
     */
    public Long getParentId() {
        return parentId;
    }

    /**
     * @param parentId
     */
    public void setParentId(Long parentId) {
        this.parentId = parentId;
    }

    /**
     * @return the orderCount
     */
    public Integer getOrderCount() {
        return orderCount;
    }

    /**
     * @param orderCount
     */
    public void setOrderCount(Integer orderCount) {
        this.orderCount = orderCount;
    }

    /**
     * @return the projectId
     */
    public Long getProjectId() {
        return projectId;
    }

    /**
     * @param projectId
     */
    public void setProjectId(Long projectId) {
        this.projectId = projectId;
    }

    /**
     * @return the children
     */
    public List<TreeDTO> getChildren() {
        return children;
    }

    /**
     * @param children
     */
    public void setChildren(List<TreeDTO> children) {
        this.children = children;
    }

}

1. 先将parentId为空的节点设置为projectId。

    /**
     * 将根目录节点的设置为projectId
     */
    private void setRootTreeNode(List<TreeDTO> treeList, Long projectId) {

        // 没有parentId，即将projectId作为parentId
        for (TreeDTO dto : treeList) {

            Long parentId = dto.getParentId();

            if (parentId == null) {
                dto.setParentId(projectId);
            }
        }
    }

2. 返回树型结构

// 构造树结构，treeList为上面的JSON节点的List形式，返回之后即为树型
JSONArray resultTree = listInfoToTree(JSONArray.parseArray(JSON.toJSONString(treeList)), "id", "parentId", "children");

3. 将文中开始列出的list转为tree

   /**
     * 将JSONArray数组转为树状结构
     * 
     * @param arr
     *            需要转化的数组
     * @param id
     *            数据唯一的标识键值名称
     * @param pid
     *            父id唯一标识键值名称
     * @param child
     *            子节点名称
     * 
     * @return array
     */
    private JSONArray listInfoToTree(JSONArray arr, String id, String pid, String child) {

        JSONArray ret = new JSONArray();

        // 将数据直接构建成为hash
        JSONObject hash = new JSONObject();

        // 节点大小
        int size = arr.size();

        // 将数组转为Object的形式，key为数组中的id，并组装为map
        for (int i = 0; i < size; i++) {

            JSONObject json = (JSONObject) arr.get(i);
            hash.put(json.getString(id), json);
        }

        // 遍历结果集
        for (int j = 0; j < size; j++) {

            // 单条记录
            JSONObject nodeVal = (JSONObject) arr.get(j);

            // 在hash中取出key为单条记录中pid的值
            JSONObject hashParent = (JSONObject) hash.get(nodeVal.get(pid).toString());

            // 如果记录的pid存在，则说明它有父节点，将她添加到孩子节点的集合中（这里与刚才所说的所有parentId为空的节点填充一个projectid并不冲突，因为当填入projectId的时候，hashParent是get不到值的）
            if (hashParent != null) {

                // 构造child属性
                if (hashParent.get(child) != null) {

                    JSONArray chArr = (JSONArray) hashParent.get(child);
                    chArr.add(nodeVal);
                    hashParent.put(child, chArr);
                } else {
					
                    JSONArray chArr = new JSONArray();
                    chArr.add(nodeVal);
                    hashParent.put(child, chArr);
                }
            } else {
                ret.add(nodeVal);
            }
        }
        return ret;
    }

4. PostMan返回结果：

"data": [
            {
                "orderCount": 0,
                "id": "661661966154199040",
                "text": "迄病蚤莎紊脸液板锌猿灯金",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 1,
                "id": "661662130646413312",
                "text": "虽曙拱抿蛊绩簧蛛伞杀",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 2,
                "id": "661662428978868224",
                "text": "粳野赣下喉迎醇丛攘颓",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 4,
                "id": "661661793088827392",
                "text": "仰儡辖龙蒸锰篡带伞蚂",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 5,
                "id": "661661918448185344",
                "text": "殃书您衡牛阎农鸣",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 6,
                "id": "772919255229394944",
                "text": "154641",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 7,
                "id": "661661956607963136",
                "text": "赊于毋钱永患几伤凛婆辉雪",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 8,
                "id": "661661957128056832",
                "text": "刀脑散郎蒙铀饼每舍誓刺卷",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "children": [
                    {
                        "orderCount": 2,
                        "id": "772919473459032064",
                        "text": "154642",
                        "projectId": "741917334711331456",
                        "parentId": "653294833572617088"
                    },
                    {
                        "orderCount": 3,
                        "id": "772917879430574080",
                        "text": "15464",
                        "projectId": "741917334711331456",
                        "parentId": "653294833572617088"
                    }
                ],
                "orderCount": 11,
                "id": "653294833572617088",
                "text": "测试链22",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 12,
                "id": "653370321808759680",
                "text": "sfdas",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 13,
                "id": "653385876393532288",
                "text": "哈哈哈哈哈哈哈哈",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            }
        ]