树结构处理，list和tree互转

1、实体类

package com.iot.common.test.entity;import lombok.Data;import java.util.List;/*** @description:* @author:zilong* @date:2023/9/8*/
@Data
public class Node {//idprivate String id;//父节点idprivate String pId;//名称private String name;//编码private String code;//层级private String level;private List<Node> children;public Node(String id, String pId, String name, String code, String level) {this.id = id;this.pId = pId;this.name = name;this.code = code;this.level = level;}public Node() {}
}

2、工具类

package com.iot.common.util;import com.alibaba.fastjson.JSON;
import com.baomidou.mybatisplus.core.toolkit.support.SFunction;
import com.iot.common.test.entity.Node;
import lombok.SneakyThrows;import java.lang.invoke.SerializedLambda;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.BiConsumer;
import java.util.function.Function;
import java.util.stream.Collectors;/*** 树工具类*/public class TreeUtil {/*** 基础数据转树结构Map版本（速度比递归要快很多）** @param sourceList  需转换的数据* @param getId       主键* @param getParentId 父id （父id必须和主键相同类型）* @param getChildren 子集* @param setChildren 子集* @return tree*/public static <T, R> List<T> listToTree(List<T> sourceList, Function<T, R> getId, Function<T, R> getParentId,Function<T, List<T>> getChildren, BiConsumer<T, List<T>> setChildren) {Map<R, T> oldMap = sourceList.stream().collect(Collectors.toMap(getId, T -> T));List<T> treeList = new ArrayList<>();sourceList.forEach(tree -> {T parent = oldMap.get(getParentId.apply(tree));if (parent == null) {treeList.add(tree);} else {List<T> ch = getChildren.apply(parent);if (ch == null) {ch = new ArrayList<>();}ch.add(tree);setChildren.accept(parent, ch);}});return treeList;}/*** 树结构转父子排序列表且按父在前，子在后，进行排序。** @param treeList    父子树列表（带有id、parentId和children的模型列表）* @param getId* @param getParentId* @param getChildren* @param setChildren* @param <T>* @param <R>* @return*/public static <T, R> List<T> treeListToSortList(List<T> treeList, Function<T, R> getId, Function<T, R> getParentId,Function<T, List<T>> getChildren, BiConsumer<T, List<T>> setChildren) {// 先整成树形结构List<T> list = listToTree(treeList, getId, getParentId, getChildren, setChildren);List<T> sortList = new ArrayList<>();tree2List(sortList, list.get(0), getChildren, setChildren);return sortList;}/*** 树结构转列表** @param result      结果容器* @param t           树顶部元素* @param getChildren* @param <T>*/private static <T> void tree2List(List<T> result, T t, Function<T, List<T>> getChildren, BiConsumer<T, List<T>> setChildren) {//根据条件判断是否需要添加至列表result.add(t);List<T> children = getChildren.apply(t);// 将children置成空setChildren.accept(t, null);//没有子级if (children == null || children.size() == 0) {return;}//存在子级，递归调用for (T child : children) {tree2List(result, child, getChildren, setChildren);}}/*** 基础数据集转树结构** @param baseList      树结构的基础数据集* @param getIdFn       获取主键的函数* @param getParentIdFn 获取父节点的函数* @param getChildrenFn 获取子集的函数* @param <T>           t* @param <R>           r* @return t*/@SneakyThrowspublic static <T, R> List<T> treeOut(List<T> baseList, Function<T, R> getIdFn, Function<T, R> getParentIdFn, SFunction<T, R> getChildrenFn) {/*所有元素的Id*/List<Object> ids = baseList.stream().map(getIdFn).collect(Collectors.toList());/*查出所有顶级节点*/List<T> topLevel = baseList.stream().filter(x -> {R apply = getParentIdFn.apply(x);return !ids.contains(apply);}).collect(Collectors.toList());return TreeUtil.recursion(topLevel, baseList, getIdFn, getParentIdFn, getChildrenFn);}/*** 指定顶级元素的基础数据集转树结构** @param list* @param top* @param getIdFn* @param getParentIdFn* @param getChildrenFn* @param <T>* @param <R>* @return*/@SneakyThrowspublic static <T, R> List<T> treeOutWithTop(List<T> list, T top, Function<T, R> getIdFn, Function<T, R> getParentIdFn, SFunction<T, R> getChildrenFn) {ArrayList<T> ts = new ArrayList<>();ts.add(top);return TreeUtil.recursion(ts, list, getIdFn, getParentIdFn, getChildrenFn);}@SneakyThrowsprivate static <T, R> List<T> recursion(List<T> superLevel, List<T> list, Function<T, R> getIdFn, Function<T, R> getParentIdFn, SFunction<T, R> getChildrenFn) {//获取setChildren的MethodMethod writeReplaceMethod = getChildrenFn.getClass().getDeclaredMethod("writeReplace");boolean accessible = writeReplaceMethod.isAccessible();writeReplaceMethod.setAccessible(true);SerializedLambda serializedLambda = (SerializedLambda) writeReplaceMethod.invoke(getChildrenFn);writeReplaceMethod.setAccessible(accessible);String setMethodName = serializedLambda.getImplMethodName().replaceFirst("g", "s");Method setMethod = Class.forName(serializedLambda.getImplClass().replace("/", ".")).getDeclaredMethod(setMethodName, List.class);for (T t : superLevel) {List<T> children = list.stream().filter(x -> {R apply = getParentIdFn.apply(x);R apply1 = getIdFn.apply(t);return apply.equals(apply1);}).collect(Collectors.toList());if (children.size() <= 0) {continue;}List<T> recursion = recursion(children, list, getIdFn, getParentIdFn, getChildrenFn);setMethod.invoke(t, recursion);}return superLevel;}/*** 将列表转换为树形结构* 注：此方法的根节点的pid需要为null** @param nodeList 列表* @return 树形结构*/public static List<Node> buildTree(List<Node> nodeList) {// 存储所有节点Map<String, Node> nodeMap = new HashMap<>(nodeList.size());// 存储根节点List<Node> rootList = new ArrayList<>();// 将所有节点存储到map中，并找出根节点for (Node node : nodeList) {nodeMap.put(node.getId(), node);if (node.getPId() == null) {rootList.add(node);}}// 遍历所有节点，将子节点添加到父节点的children中for (Node node : nodeList) {String pId = node.getPId();if (pId != null) {Node parentNode = nodeMap.get(pId);if (parentNode != null) {if (parentNode.getChildren() == null) {parentNode.setChildren(new ArrayList<>());}parentNode.getChildren().add(node);}}}return rootList;}public static void main(String[] args) {ArrayList<Node> list = new ArrayList<Node>() {{add(new Node("1", "0", "A", "1", "1"));add(new Node("2", "0", "B", "2", "1"));add(new Node("3", "1", "A-1", "11", "2"));add(new Node("4", "1", "A-2", "12", "2"));add(new Node("5", "3", "A-1-1", "111", "3"));add(new Node("6", "5", "A-1-1-1", "1111", "4"));add(new Node("7", "6", "A-1-1-1-1", "11111", "5"));add(new Node("8", "2", "B-1", "21", "2"));add(new Node("9", "8", "B-1-1", "211", "3"));add(new Node("10", "9", "B-1-1-1", "2111", "4"));}};//使用工具类 treeOut:List<Node> result = TreeUtil.treeOut(list, Node::getId, Node::getPId, Node::getChildren);System.out.println("-----【treeOut】-----");System.out.println(JSON.toJSONString(result));//使用工具类 listToTree（Map）:List<Node> result1 = TreeUtil.listToTree(list, Node::getId, Node::getPId, Node::getChildren, Node::setChildren);System.out.println("-----【listToTree】-----");System.out.println(JSON.toJSONString(result1));//使用工具类 treeOutWithTop:Node top = new Node();top.setId("3");List<Node> result2 = TreeUtil.treeOutWithTop(list, top, Node::getId, Node::getPId, Node::getChildren);System.out.println("-----【treeOutWithTop】-----");System.out.println(JSON.toJSONString(result2));//使用工具类 buildTree:List<Node> result3 = TreeUtil.buildTree(list);System.out.println("-----【buildTree】-----");System.out.println(JSON.toJSONString(result3));}}