Java構造前端vue使用的樹（或者使用Java構造常用的部門樹等）

  Web項目開發中，由於前端框架的限制，很多時候需要將返回的數據加工後再返回給前端。最典型的就是返回一棵部門層級關係的樹。下面即是一棵帶有層級的文檔標題樹，和我們書籍的目錄結構一樣。

  在樹的結構中，每一個節點都需要有一顆父級節點，即使是頂級節點，也需要給其父節點賦值。比如，在下面的帶有父子關係的線性結構中，有些id的parentId是null的，此時就需要將parentId爲null賦值爲projectId。同時使用了fastjson作爲輔助工具，具有一定的通用性。其數值如下：

"data": [
            {
                "id": "661661966154199040",
                "text": null,
                "parentId": null,//父級id爲空，需要將其賦值爲projectId
                "orderCount": 0,
                "projectId": "741917334711331456",
                "children": null//下級節點
            },
            {
                "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
            }
        ]

樹的DTO結構如下，注意children:

public class TreeDTO {

    /** 兒子id **/
    private Long id;

    /** 附帶文本 **/
    private String text;

    /** 父級id **/
    private Long parentId;

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

    /** 項目id **/
    private Long projectId;

    /** 孩子節點 **/
    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. 先將parentId爲空的節點設置爲projectId。

    /**
     * 將根目錄節點的設置爲projectId
     */
    private void setRootTreeNode(List<TreeDTO> treeList, Long projectId) {

        // 沒有parentId，即將projectId作爲parentId
        for (TreeDTO dto : treeList) {

            Long parentId = dto.getParentId();

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

2. 返回樹型結構

// 構造樹結構，treeList爲上面的JSON節點的List形式，返回之後即爲樹型
JSONArray resultTree = listInfoToTree(JSONArray.parseArray(JSON.toJSONString(treeList)), "id", "parentId", "children");

3. 將文中開始列出的list轉爲tree

   /**
     * 將JSONArray數組轉爲樹狀結構
     * 
     * @param arr
     *            需要轉化的數組
     * @param id
     *            數據唯一的標識鍵值名稱
     * @param pid
     *            父id唯一標識鍵值名稱
     * @param child
     *            子節點名稱
     * 
     * @return array
     */
    private JSONArray listInfoToTree(JSONArray arr, String id, String pid, String child) {

        JSONArray ret = new JSONArray();

        // 將數據直接構建成爲hash
        JSONObject hash = new JSONObject();

        // 節點大小
        int size = arr.size();

        // 將數組轉爲Object的形式，key爲數組中的id，並組裝爲map
        for (int i = 0; i < size; i++) {

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

        // 遍歷結果集
        for (int j = 0; j < size; j++) {

            // 單條記錄
            JSONObject nodeVal = (JSONObject) arr.get(j);

            // 在hash中取出key爲單條記錄中pid的值
            JSONObject hashParent = (JSONObject) hash.get(nodeVal.get(pid).toString());

            // 如果記錄的pid存在，則說明它有父節點，將她添加到孩子節點的集合中（這裏與剛纔所說的所有parentId爲空的節點填充一個projectid並不衝突，因爲當填入projectId的時候，hashParent是get不到值的）
            if (hashParent != null) {

                // 構造child屬性
                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返回結果：

"data": [
            {
                "orderCount": 0,
                "id": "661661966154199040",
                "text": "迄病蚤莎紊臉液板鋅猿燈金",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 1,
                "id": "661662130646413312",
                "text": "雖曙拱抿蠱績簧蛛傘殺",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 2,
                "id": "661662428978868224",
                "text": "粳野贛下喉迎醇叢攘頹",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 4,
                "id": "661661793088827392",
                "text": "仰儡轄龍蒸錳篡帶傘螞",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 5,
                "id": "661661918448185344",
                "text": "殃書您衡牛閻農鳴",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 6,
                "id": "772919255229394944",
                "text": "154641",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 7,
                "id": "661661956607963136",
                "text": "賒於毋錢永患幾傷凜婆輝雪",
                "projectId": "741917334711331456",
                "parentId": "741917334711331456"
            },
            {
                "orderCount": 8,
                "id": "661661957128056832",
                "text": "刀腦散郎蒙鈾餅每舍誓刺卷",
                "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": "測試鏈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"
            }
        ]