Java 處理樹形結構數據

在寫項目中后台管理可能需要一些動態菜單樹，所以在此記錄一下先看下json數據格式

{
  "reason": "SUCCESS",
  "code": 200,
  "data": [
    {
      "id": "5",
      "labelName": "測試4",
      "parentId": null,
      "cheaked": "false",
      "children": [
        {
          "id": "6",
          "labelName": "標簽測試",
          "parentId": "5",
          "cheaked": "false",
          "children": []
        },
        {
          "id": "11",
          "labelName": "二級",
          "parentId": "5",
          "cheaked": "false",
          "children": []
        }
      ]
    },
    {
      "id": "7",
      "labelName": "測試五級",
      "parentId": null,
      "cheaked": "false",
      "children": [
        {
          "id": "8",
          "labelName": "測試四級",
          "parentId": "7",
          "cheaked": "false",
          "children": [
            {
              "id": "9",
              "labelName": "測試三級",
              "parentId": "8",
              "cheaked": "false",
              "children": []
            }
          ]
        }
      ]
    },
    {
      "id": "10",
      "labelName": "一級",
      "parentId": null,
      "cheaked": "false",
      "children": []
    }
  ],
  "message": null
}

1.先分析一下：當一行數據parentId是空的 肯定是第一層菜單，若有一行parentId是這行的Id那么就是這行的孩子

實體類

package com.cmbchina.ccd.itpm.label.entity;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Transient;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;

/**
 * @Author zly
 * @Date 2019/9/27 14:17
 */
@Entity
@Table(name = "asset_label")
public class Label implements Serializable{
    @Id
    private String id;
    private String labelName;
    private String parentId;
    private String cheaked;
    @Transient
    private List<Label> children = new ArrayList<>();

    public Label(String id, String labelName, String parentId, List<Label> children) {
        this.id = id;
        this.labelName = labelName;
        this.parentId = parentId;
        this.children = children;
    }

    public Label() {
    }
    public String getCheaked() {
        return cheaked;
    }

    public void setCheaked(String cheaked) {
        this.cheaked = cheaked;
    }

    @Override
    public String toString() {
        return "Label{" + "id='" + id + '\'' + ", labelName='" + labelName + '\'' + ", parentId='" + parentId + '\'' +
               ", cheaked='" + cheaked + '\'' + ", children=" + children + '}';
    }

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

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

    public String getId() {
        return id;
    }

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

    public String getLabelName() {
        return labelName;
    }

    public void setLabelName(String labelName) {
        this.labelName = labelName;
    }

    public String getParentId() {
        return parentId;
    }

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

建表語句

CREATE TABLE `asset_label` (
  `id` int(255) NOT NULL AUTO_INCREMENT COMMENT '菜單Id',
  `labelName` varchar(255) DEFAULT NULL COMMENT '菜單名稱',
  `parentId` varchar(255) DEFAULT NULL COMMENT '父級ID',
  `cheaked` varchar(255) DEFAULT 'false' COMMENT '是否勾選',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=12 DEFAULT CHARSET=utf8;

重點來了 邏輯代碼處理

 public R getAll() {
        List<Label> labelList = labelDao.getLabelList();
        return R.ok(makeTreeLabelDto(labelList));
    }

    //構建菜單樹
    public List<Label> makeTreeLabelDto(List<Label> labelList) {
        List<Label> firstLabelDto = new ArrayList<>();
        Map<String, Label> labelMap = new HashMap<>();
        for (Label label : labelList) {
            labelMap.put(label.getId(), label);
            //判斷是否有父節點 (沒有父節點本身就是個父菜單)
            if (label.getParentId() == null) {
                firstLabelDto.add(label);
            }
            //找出不是父級菜單的且集合中包括其父菜單ID
            if (label.getParentId() != null && labelMap.containsKey(label.getParentId())) {
                labelMap.get(label.getParentId()).getChildren().add(label);
            }
        }
        return firstLabelDto;
    }

 labelDao.getLabelList()這個方法就是將數據庫所有數據查詢出來沒有貼出主要看構建樹形結構的邏輯代碼
這樣就可以實現文章開頭中的數據格式