一、前言

????在后臺代碼的開發(fā)中端壳，經(jīng)常碰到有父子關(guān)聯(lián)的表設(shè)計(jì)告丢，前端要求在后臺數(shù)據(jù)以樹形封裝進(jìn)行返回，因此如何建樹损谦，或者如何更優(yōu)雅的建樹成了后臺開發(fā)工作中繞不過去的一個(gè)坎岖免，根據(jù)工作所需，這里做下總結(jié)照捡，以堪后由颅湘。

（推薦方式二）

二、方法

1.方式一：獨(dú)立對象建樹

1.1 封裝獨(dú)立對象TreeNode

package cn.keyidea.common.bean;

import io.swagger.v3.oas.annotations.media.Schema;
import lombok.Data;

import java.util.List;

/**
 * 樹節(jié)點(diǎn)實(shí)體
 */
@Data
@Schema(name = "TreeNode", description = "樹節(jié)點(diǎn)實(shí)體")
public class TreeNode {

    @Schema(description = "節(jié)點(diǎn)id", requiredMode = Schema.RequiredMode.REQUIRED)
    private Integer id;

    @Schema(description = "節(jié)點(diǎn)標(biāo)題", requiredMode = Schema.RequiredMode.REQUIRED)
    private String title;

    @Schema(description = "子節(jié)點(diǎn)", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private List<TreeNode> children;

    @Schema(description = "父節(jié)點(diǎn)id", requiredMode = Schema.RequiredMode.REQUIRED)
    private Integer parentId;

    /**
     * 節(jié)點(diǎn)是否初始為選中狀態(tài)（如果開啟復(fù)選框的話）栗精，默認(rèn) false
     */
    @Schema(description = "節(jié)點(diǎn)是否初始為選中狀態(tài)（如果開啟復(fù)選框的話）闯参，默認(rèn) false", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private Boolean checked;

    @Schema(description = "URL地址", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private String url;

    @Schema(description = "類型", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private Integer type;

    @Schema(description = "code碼", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private String code;

    @Schema(description = "圖標(biāo)", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private String icon;

    @Schema(description = "路由地址", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    private String component;
}

1.2 建樹工具類

package cn.keyidea.common.util;

import cn.keyidea.common.bean.TreeNode;

import java.util.ArrayList;
import java.util.List;

/**
 * Tree工具類
 */
public class TreeUtil {
    /**
     * 兩層循環(huán)實(shí)現(xiàn)建樹
     *
     * @param treeNodes 傳入的樹節(jié)點(diǎn)列表
     * @return
     */
    public static List<TreeNode> bulidTree(List<TreeNode> treeNodes) {

        List<TreeNode> trees = new ArrayList<TreeNode>();

        for (TreeNode treeNode : treeNodes) {

            if (0 == treeNode.getParentId()) {
                trees.add(treeNode);
            }

            for (TreeNode it : treeNodes) {
                if (null != it.getParentId()) {
                    if (it.getParentId().equals(treeNode.getId())) {
                        if (treeNode.getChildren() == null) {
                            treeNode.setChildren(new ArrayList<TreeNode>());
                        }
                        treeNode.getChildren().add(it);
                    }
                }
            }
        }
        return trees;
    }
}

2.方式二：原生對象建樹（推薦）

2.1 以Entity實(shí)體作為自身節(jié)點(diǎn)

由于菜單一般設(shè)計(jì)成帶有父子項(xiàng)，因此這里以菜單對象做示例悲立。

package cn.keyidea.sys.entity;

import cn.keyidea.common.annotation.EnumValue;
import cn.keyidea.common.bean.BaseModel;
import cn.keyidea.common.valid.GroupAdd;
import cn.keyidea.common.valid.GroupUpdate;
import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableLogic;
import com.baomidou.mybatisplus.annotation.TableName;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonProperty;
import io.swagger.v3.oas.annotations.media.Schema;
import jakarta.persistence.Column;
import jakarta.persistence.Entity;
import jakarta.persistence.Table;
import jakarta.persistence.Transient;
import jakarta.validation.constraints.NotBlank;
import jakarta.validation.constraints.NotNull;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.NoArgsConstructor;
import lombok.experimental.SuperBuilder;
import org.hibernate.annotations.Comment;

import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

/**
 * 系統(tǒng)菜單
 *
 * @author qyd
 * @date 2022-10-17
 */
@SuperBuilder
@AllArgsConstructor
@NoArgsConstructor
@Data
@EqualsAndHashCode(callSuper = true)
@TableName("sys_menu")
@Schema(name = "SysMenu", description = "系統(tǒng)菜單")
@Entity
@Table(name = "sys_menu")
@Comment("系統(tǒng)菜單表")
public class SysMenu extends BaseModel {

    @NotNull(message = "父菜單不能為NULL", groups = {GroupAdd.class, GroupUpdate.class})
    @Schema(description = "父菜單ID鹿寨，一級菜單為0", requiredMode = Schema.RequiredMode.REQUIRED, example = "0")
    @Column(name = "parent_id", columnDefinition = "int(10) not null COMMENT '父菜單ID，一級菜單為0'")
    private Integer parentId;

    // name ==> label
    @NotBlank(message = "菜單名稱不能為空", groups = {GroupAdd.class, GroupUpdate.class})
    @Schema(description = "菜單名稱", requiredMode = Schema.RequiredMode.REQUIRED)
    @Column(name = "label", columnDefinition = "varchar(100) not null COMMENT '菜單名稱'")
    private String label;

    @NotNull(message = "菜單類型不能為NULL", groups = {GroupAdd.class, GroupUpdate.class})
    @EnumValue(intValues = {0, 1, 2, 3}, message = "菜單類型不符合條件")
    @Schema(description = "菜單類型：0-系統(tǒng)薪夕，1-目錄脚草，2-菜單，3-按鈕", requiredMode = Schema.RequiredMode.REQUIRED)
    @Column(name = "type", columnDefinition = "int(2) not null COMMENT '菜單類型：0-系統(tǒng)寥殖，1-目錄玩讳，2-菜單，3-按鈕'")
    private Integer type;

    @Schema(description = "菜單圖標(biāo)url", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @Column(name = "icon", columnDefinition = "varchar(100) COMMENT '菜單圖標(biāo)url'")
    private String icon;

    // url ==> key
    // 數(shù)據(jù)庫存儲url嚼贡，返回給前端使用key（key為MySQL關(guān)鍵字無法作為存儲字段）
    @JsonProperty("key")
    @Schema(description = "菜單URL", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @Column(name = "url", columnDefinition = "varchar(100) COMMENT '菜單URL'")
    private String url;

    @Schema(description = "菜單路由地址", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @Column(name = "component", columnDefinition = "varchar(100) COMMENT '菜單路由地址'")
    private String component;

    @Schema(description = "權(quán)限標(biāo)識熏纯，如：user:list", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @Column(name = "perms", columnDefinition = "varchar(100) COMMENT '權(quán)限標(biāo)識，如：user:list'")
    private String perms;

    @NotNull(message = "排序號不能為NULL", groups = {GroupAdd.class, GroupUpdate.class})
    @Schema(description = "排序號", requiredMode = Schema.RequiredMode.REQUIRED)
    @Column(name = "order_num", columnDefinition = "int(10) not null COMMENT '排序號'")
    private Integer orderNum;

    @TableLogic
    @JsonIgnore
    @Column(name = "del_flag", columnDefinition = "int(2) not null COMMENT '刪除狀態(tài)：0-正常粤策，1-刪除'")
    @TableField(value = "del_flag", fill = FieldFill.INSERT)
    private Integer delFlag;

    // ---------------------- 以下非數(shù)據(jù)庫字段 ----------------------

    @Schema(description = "子孩子", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @TableField(exist = false)
    @Transient
    private List<SysMenu> children;

    /**
     * 建樹
     *
     * @param list     待建樹集合
     * @param parentId 父節(jié)點(diǎn)樟澜，一般為0作為父節(jié)點(diǎn)
     * @return 返回樹
     */
    public static List<SysMenu> streamToTree(List<SysMenu> list, Integer parentId) {
        return list.stream()
                .filter(parent -> Objects.equals(parent.getParentId(), parentId))
                .peek(child -> child.setChildren(streamToTree(list, child.getId())))
                .collect(Collectors.toList());
    }
}

2.2 涉及BaseModel類

package cn.keyidea.common.bean;

import cn.keyidea.common.valid.GroupChangePwd;
import cn.keyidea.common.valid.GroupCustomWithId;
import cn.keyidea.common.valid.GroupUpdate;
import com.alibaba.fastjson.annotation.JSONField;
import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.TableField;
import com.fasterxml.jackson.annotation.JsonFormat;
import io.swagger.v3.oas.annotations.media.Schema;
import jakarta.persistence.*;
import jakarta.validation.constraints.NotNull;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.experimental.SuperBuilder;
import org.springframework.data.jpa.domain.support.AuditingEntityListener;

import java.io.Serial;
import java.io.Serializable;
import java.util.Date;


/**
 * 實(shí)體父類
 * <p>
 * 特殊說明：
 * 繼承此基類的實(shí)體類，如果使用lombok的@Data注解時(shí)叮盘，主要同時(shí)添加@EqualsAndHashCode(callSuper = true)注解
 * 1)注解@EqualsAndHashCode(callSuper = true)秩贰，就是用自己的屬性和從父類繼承的屬性來生成hashcode；
 * 2)注解@EqualsAndHashCode(callSuper = false)柔吼，就是只用自己的屬性來生成hashcode毒费；
 * 3)@Data相當(dāng)于@Getter @Setter @RequiredArgsConstructor @ToString @EqualsAndHashCode這5個(gè)注解的合集, 和@EqualsAndHashCode默認(rèn)是false。
 * <p>
 * MappedSuperclass注解說明：
 * 1.@MappedSuperclass注解僅僅能標(biāo)準(zhǔn)在類上愈魏；這個(gè)注解標(biāo)識在父類上面的觅玻，用來標(biāo)識父類
 * 2.標(biāo)注為@MappedSuperclass的類將不是一個(gè)完整的實(shí)體類想际，他將不會映射到數(shù)據(jù)庫表，可是他的屬性都將映射到其子類的數(shù)據(jù)庫字段中
 * 3.標(biāo)注為@MappedSuperclass的類不能再標(biāo)注@Entity或@Table注解
 * <p>
 * EntityListeners注解及相關(guān)說明：
 * EntityListeners：該注解用于指定Entity或者superclass上的回調(diào)監(jiān)聽類
 * AuditingEntityListener：這是一個(gè)JPA Entity Listener溪厘，用于捕獲監(jiān)聽信息胡本，當(dāng)Entity發(fā)生持久化和更新操作時(shí)
 *
 * @author qyd
 * @date 2022-10-17
 */
@SuperBuilder   // @SuperBuilder支持對基類成員屬性的構(gòu)造；如果子類繼承了BaseModel畸悬，也需要使用該注解
@AllArgsConstructor // 全參構(gòu)造函數(shù)
@NoArgsConstructor  // 空參構(gòu)造函數(shù)
@Data
@MappedSuperclass
@EntityListeners(AuditingEntityListener.class)
@Schema(name = "BaseModel", description = "實(shí)體父類")
public class BaseModel implements Serializable {

    @Serial
    private static final long serialVersionUID = 1L;

    @NotNull(message = "ID不能為NUll", groups = {GroupUpdate.class, GroupChangePwd.class, GroupCustomWithId.class})
    @Schema(description = "主鍵ID", requiredMode = Schema.RequiredMode.REQUIRED, example = "1")
    @Id
    @Column(name = "id", columnDefinition = "int(10) COMMENT '自增長ID'")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Schema(description = "創(chuàng)建時(shí)間", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    @Column(name = "create_time", updatable = false, columnDefinition = "datetime not null COMMENT '創(chuàng)建時(shí)間'")
    @TableField(value = "create_time", fill = FieldFill.INSERT)
    @JSONField(format = "yyyy-MM-dd HH:mm:ss")
    private Date createTime;

    @Schema(description = "創(chuàng)建人ID", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @Column(name = "create_by", updatable = false, columnDefinition = "int(10) not null COMMENT '創(chuàng)建人ID'")
    @TableField(value = "create_by", fill = FieldFill.INSERT)
    private Integer createBy;

    @Schema(description = "更新時(shí)間", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "GMT+8")
    @Column(name = "update_time", columnDefinition = "datetime COMMENT '更新時(shí)間'")
    @TableField(value = "update_time", fill = FieldFill.UPDATE)
    @JSONField(format = "yyyy-MM-dd HH:mm:ss")
    private Date updateTime;

    @Schema(description = "更新人ID", requiredMode = Schema.RequiredMode.NOT_REQUIRED)
    @Column(name = "update_by", columnDefinition = "int(10) COMMENT '更新人ID'")
    @TableField(value = "update_by", fill = FieldFill.UPDATE)
    private Integer updateBy;

}

3.方式一 vs 方式二

對于方式二來說侧甫，新增的字段主要就是在原生對象中新增private List<T> children;， 然后新增靜態(tài)方法streamToTree蹋宦，并且能完美支持原生所有字段披粟，所差的是，如果有10個(gè)類都需要建樹的話妆档，那么每個(gè)類都需要寫同樣的方法僻爽。不過對于方式一來說，如果真存在10個(gè)類贾惦，并且每個(gè)類字段都存在差異性胸梆，那么方式一中的TreeNode的冗余字段將變的非常之多。

END