1.情景展示

接著上一篇講，在上一篇我們已經將資料通過遞迴轉成了樹形結構。

如何將樹形結構轉非樹形結構？（仍然按照樹形層級關係進行平鋪顯示）

[{
		name = 根節點,
		childList = [{
				name = 一級節點1,
				childList = [{
						name = 二級節點1.1,
						childList = [],
						id = 3,
						parentId = 2
					}, {
						name = 二級節點1.2,
						childList = [],
						id = 4,
						parentId = 2
					}, {
						name = 二級節點1.3,
						childList = [],
						id = 5,
						parentId = 2
					}
				],
				id = 2,
				parentId = 1
			}, {
				name = 一級節點2,
				childList = [{
						name = 二級節點2.1,
						childList = [{
								name = 三級節點2.1.1,
								childList = [],
								id = 9,
								parentId = 7
							}, {
								name = 三節點2.1.2,
								childList = [],
								id = 10,
								parentId = 7
							}
						],
						id = 7,
						parentId = 6
					}, {
						name = 二級節點2.2,
						childList = [],
						id = 8,
						parentId = 6
					}
				],
				id = 6,
				parentId = 1
			}, {
				name = 一級節點3,
				childList = [{
						name = 二級節點3.1,
						childList = [{
								name = 三級節點3.1.1,
								childList = [{
										name = 四級節點3.1.1.1,
										childList = [{
												name = 五級節點3.1.1.1.1,
												childList = [],
												id = 15,
												parentId = 14
											}
										],
										id = 14,
										parentId = 13
									}
								],
								id = 13,
								parentId = 12
							}
						],
						id = 12,
						parentId = 11
					}
				],
				id = 11,
				parentId = 1
			}
		],
		id = 1,
		parentId = 0
	}
]
 

2.具體分析

可以通過棧Stack來完成。

3.解決方案

程式碼實現

/*
 * 將父節點下的子節點進行由巢狀改成平鋪
 * @description: 按照層級關係，將巢狀改成平鋪
 * @param: root 巢狀資料
 * @return: java.util.ArrayList<java.util.Map<java.lang.String,java.lang.Object>>
 * 平鋪資料
 */
public static ArrayList<Map<String, Object>> tileTraversal(Map<String, Object> root) {
    ArrayList<Map<String, Object>> res = new ArrayList<>();
    if (root == null) {
        return res;
    }

    Stack<Map<String, Object>> stack = new Stack<>();
    stack.push(root);
    while (!stack.empty()) {
        Map<String, Object> temp = stack.pop();
        Map<String, Object> copyMap = new HashMap<>(temp.size());
        // 複製當前節點
        copyMap.putAll(temp);
        // 移除map（該節點）當中的子節點
        copyMap.remove("childList");
        // 將此節點放到集合當中
        res.add(copyMap);

        // 當前節點，存在子節點
        if (temp.get("childList") != null && ((List<Map<String, Object>>) temp.get("childList")).size() > 0) {
            // ((List<Map<String, Object>>) temp.get("childList")).forEach(m -> stack.push(m));

            List<Map<String, Object>> list = (List<Map<String, Object>>) temp.get("childList");
            for (int i = list.size() - 1; i >= 0; i--) {
                stack.push(list.get(i));
            }
        }
    }
    return res;
}
 

呼叫

// mapList是樹形結構（已經存在的資料）
List<Map<String, Object>> tileList = new ArrayList<>();
mapList.forEach(m -> tileList.addAll(tileTraversal(m)));
System.out.println(tileList);

[{name=根節點, id=1, parentId=0}, {name=一級節點1, id=2, parentId=1}, {name=二級節點1.1, id=3, parentId=2}, {name=二級節點1.2, id=4, parentId=2}, {name=二級節點1.3, id=5, parentId=2}, {name=一級節點2, id=6, parentId=1}, {name=二級節點2.1, id=7, parentId=6}, {name=三級節點2.1.1, id=9, parentId=7}, {name=三節點2.1.2, id=10, parentId=7}, {name=二級節點2.2, id=8, parentId=6}, {name=一級節點3, id=11, parentId=1}, {name=二級節點3.1, id=12, parentId=11}, {name=三級節點3.1.1, id=13, parentId=12}, {name=四級節點3.1.1.1, id=14, parentId=13}, {name=五級節點3.1.1.1.1, id=15, parentId=14}]
 

4.效果展示

轉JSON

System.out.println(JSON.toJSON(tileList));

[{"name":"根節點","id":"1","parentId":"0"},{"name":"一級節點1","id":"2","parentId":"1"},{"name":"二級節點1.1","id":"3","parentId":"2"},{"name":"二級節點1.2","id":"4","parentId":"2"},{"name":"二級節點1.3","id":"5","parentId":"2"},{"name":"一級節點2","id":"6","parentId":"1"},{"name":"二級節點2.1","id":"7","parentId":"6"},{"name":"三級節點2.1.1","id":"9","parentId":"7"},{"name":"三節點2.1.2","id":"10","parentId":"7"},{"name":"二級節點2.2","id":"8","parentId":"6"},{"name":"一級節點3","id":"11","parentId":"1"},{"name":"二級節點3.1","id":"12","parentId":"11"},{"name":"三級節點3.1.1","id":"13","parentId":"12"},{"name":"四級節點3.1.1.1","id":"14","parentId":"13"},{"name":"五級節點3.1.1.1.1","id":"15","parentId":"14"}]

格式化

[{
	"name": "根節點",
	"id": "1",
	"parentId": "0"
},
{
	"name": "一級節點1",
	"id": "2",
	"parentId": "1"
},
{
	"name": "二級節點1.1",
	"id": "3",
	"parentId": "2"
},
{
	"name": "二級節點1.2",
	"id": "4",
	"parentId": "2"
},
{
	"name": "二級節點1.3",
	"id": "5",
	"parentId": "2"
},
{
	"name": "一級節點2",
	"id": "6",
	"parentId": "1"
},
{
	"name": "二級節點2.1",
	"id": "7",
	"parentId": "6"
},
{
	"name": "三級節點2.1.1",
	"id": "9",
	"parentId": "7"
},
{
	"name": "三節點2.1.2",
	"id": "10",
	"parentId": "7"
},
{
	"name": "二級節點2.2",
	"id": "8",
	"parentId": "6"
},
{
	"name": "一級節點3",
	"id": "11",
	"parentId": "1"
},
{
	"name": "二級節點3.1",
	"id": "12",
	"parentId": "11"
},
{
	"name": "三級節點3.1.1",
	"id": "13",
	"parentId": "12"
},
{
	"name": "四級節點3.1.1.1",
	"id": "14",
	"parentId": "13"
},
{
	"name": "五級節點3.1.1.1.1",
	"id": "15",
	"parentId": "14"
}]

說明：

事實上，使用SQL進行遞迴查詢，返回的就是這種格式的資料，即：按照層級關係排好序展示出來；

如果前端需要的是這種排好序的資料，直接返回即可；

如果需要返回樹形結構的話，見文末推薦。 

寫在最後

　　哪位大佬如若發現文章存在紕漏之處或需要補充更多內容，歡迎留言！！！

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