2024年3月17日
数据库保存的对象均为单个对象。返回前端为tree展示。
之前见过全部轮询，但是由于轮询过多导致在一万多条数据耗时较久。现在改进为先进行分组，然后再进行轮询查找对应孩子对象list。用以提高效率
huool和json可以按需引入。不影响核心功能

直接将代码展示

import java.util.List;

public class TreeNode {

    private Long id;
    private String label;
    private Long parentId;
    private List<TreeNode> children;


    public Long getId() {
        return id;
    }

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

    public String getLabel() {
        return label;
    }

    public void setLabel(String label) {
        this.label = label;
    }

    public Long getParentId() {
        return parentId;
    }

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

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

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

}

import cn.hutool.core.convert.Convert;
import com.alibaba.fastjson.JSONObject;

import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class TreeNodeUtil {
    public static void main(String[] args) {
        List<TreeNode> allList=new LinkedList<>();
        for (int i = 0; i < 20; i++) {
            TreeNode treeNode=new TreeNode();
            treeNode.setId(i+1L);
            treeNode.setLabel("label"+i);
            if (i<3){
                treeNode.setParentId(0L);
            }else if (i<8){
                treeNode.setParentId(1L);
            }else if (i<12){
                treeNode.setParentId(2L);
            }else if (i<15){
                treeNode.setParentId(5L);
            }else {
                treeNode.setParentId(6L);
            }
            allList.add(treeNode);
        }
        List<TreeNode> treeNodes = listToTree(allList, 0L);
        System.out.println("json-> " + JSONObject.toJSONString(treeNodes));
    }



    public static List<TreeNode> listToTree(List<TreeNode> allList, Long rootId) {

        Map<Long, List<TreeNode>> treeMap = allList.stream().filter(treeNode -> treeNode.getParentId()!=null).collect(Collectors.groupingBy(TreeNode::getParentId));
        if(treeMap==null){
            return new LinkedList<>();
        }
        List<TreeNode> treeNodes = treeMap.get(rootId);
        if (treeNodes!=null){
            treeNodes.sort(Comparator.comparingLong(o -> Convert.toLong(o.getId(), 0L)));
            findChildren(treeMap,treeNodes);
        }else {
            treeNodes=new LinkedList<>();
        }
        return treeNodes;
    }
// 递归获取全部childen列表
    private static void findChildren(Map<Long, List<TreeNode>> treeMap, List<TreeNode> treeNodes) {
        for (TreeNode treeNode : treeNodes) {
            Long id = treeNode.getId();
            List<TreeNode> treeNodes1 = treeMap.get(id);
            if (treeNodes1!=null){
                treeNodes1.sort(Comparator.comparingLong(o -> Convert.toLong(o.getId(), 0L)));
                treeNode.setChildren(treeNodes1);
                findChildren(treeMap,treeNodes1);
            }else {
                treeNode.setChildren(new LinkedList<>());
            }
        }
    }


}