stream流进行tree树组装

1.准备工具类。

package com.joolun.mall.util;

import com.joolun.mall.entity.TreeNode;
import lombok.experimental.UtilityClass;

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

/**
 * @author
 */
@UtilityClass
public class TreeUtil {
    /**
     * 两层循环实现建树
     *
     * @param treeNodes 传入的树节点列表
     * @return
     */
    public <T extends TreeNode> List<T> build(List<T> treeNodes, Object root) {
        List<T> trees = new ArrayList<>();
        for (T treeNode : treeNodes) {
            if (root.equals(treeNode.getParentId())) {
                trees.add(treeNode);
//                trees.sort(Comparator.comparing(TreeNode::getSort));
            }
            for (T it : treeNodes) {
                if (it.getParentId().equals(treeNode.getId())) {
                    treeNode.addChildren(it);
//                    treeNode.getChildren().sort(Comparator.comparing(TreeNode::getSort));
                }
            }
        }
        return trees;
    }

    /**
     * 使用递归方法建树
     *
     * @param treeNodes
     * @return
     */
    public <T extends TreeNode> List<T> buildByRecursive(List<T> treeNodes, Object root) {
        List<T> trees = new ArrayList<T>();
        for (T treeNode : treeNodes) {
            if (root.equals(treeNode.getParentId())) {
                trees.add(findChildren(treeNode, treeNodes));
            }
        }
        return trees;
    }

    /**
     * 递归查找子节点
     *
     * @param treeNodes
     * @return
     */
    public <T extends TreeNode> T findChildren(T treeNode, List<T> treeNodes) {
        for (T it : treeNodes) {
            if (treeNode.getId() == it.getParentId()) {
                if (treeNode.getChildren() == null) {
                    treeNode.setChildren(new ArrayList<>());
                }
                treeNode.addChildren(findChildren(it, treeNodes));
            }
        }
        return treeNode;
    }


}

2.接收实体改造

package com.joolun.mall.entity;

import lombok.Data;

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

/**
 * @author
 */
@Data
public class TreeNode {
    protected String id;
    protected String parentId;
    private Integer sort;
    protected List<TreeNode> children = new ArrayList<>();

    public void addChildren(TreeNode treeNode) {
        children.add(treeNode);
    }

    public List<TreeNode> getChildren() {
        if(children.size()<=0){
            return null;
        }
        return children;
    }
}

package com.joolun.mall.entity;

import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import lombok.EqualsAndHashCode;

import java.time.LocalDateTime;

/**
 * 商品类目
 *
 * @author www.joolun.com
 * @date 2019-08-12 11:46:28
 */
@Data
@EqualsAndHashCode(callSuper = true)
public class GoodsCategoryTree extends TreeNode {
  
    /**
     * （1：开启；0：关闭）
     */
    @ApiModelProperty(value = "1：开启；0：关闭")
    private String enable;
    /**
   * 父分类编号
   */
    @ApiModelProperty(value = "父分类编号")
    private String parentId;
    /**
   * 名称
   */
    @ApiModelProperty(value = "名称")
    private String name;
    /**
   * 描述
   */
    @ApiModelProperty(value = "描述")
    private String description;
    /**
   * 图片
   */
    @ApiModelProperty(value = "图片")
    private String picUrl;
    /**
   * 排序
   */
    @ApiModelProperty(value = "排序")
    private Integer sort;
}

3.构建树

    /**
     * 构建树
     *
     * @param entitys
     * @return
     */
    private List<GoodsCategoryTree> getTree(List<GoodsCategory> entitys) {
         //重要是下面的stream流的使用
        List<GoodsCategoryTree> treeList = entitys.stream()
                .filter(entity -> !entity.getId().equals(entity.getParentId()))
                .sorted(Comparator.comparingInt(GoodsCategory::getSort))
                .map(entity -> {
                    GoodsCategoryTree node = new GoodsCategoryTree();
                    BeanUtil.copyProperties(entity,node);//拷陪实体到组装的 tree中
                    return node;
                }).collect(Collectors.toList());
        return TreeUtil.build(treeList, CommonConstants.PARENT_ID);
    }