Java列表转树形结构工具

不废话，直接上代码

一、工具函数

可以直接使用list2tree()实现列表转树形结构

package com.server.utils.tree;import org.springframework.beans.BeanUtils;import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.function.BiConsumer;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collectors;/*** @author visy.wang* @date 2024/6/27 21:27*/
public class TreeUtil {//通过Map的方式组装树形结构（只需单次遍历即可完成）public static <T,K,R> R list2tree(List<T> list,K rootId,Function<T,K> idGetter,Function<T,K> pidGetter,Function<T,R> converter,Supplier<R> builder,BiConsumer<R,R> childAdder){Map<K, R> map = new HashMap<>();for (T t : list) {K id = idGetter.apply(t), pid = pidGetter.apply(t);//查找当前节点R node = map.get(id);if(node == null){//当前节点不存在则创建node = converter.apply(t);map.put(id, node);}else{//当前节点已存在（被其他节点以父节点加入），补全剩余字段R srcNode = converter.apply(t);BeanUtils.copyProperties(srcNode, node, getNullProperties(srcNode));}//查找父节点R parent = map.get(pid);if(parent == null){//父节点不存在，则创建父节点，并将自身添加到父节点的子节点集合中parent = builder.get();childAdder.accept(parent, node);map.put(pid, parent);}else{//父节点已存在，直接将自身添加到父节点的子节点集合中childAdder.accept(parent, node);}}return map.get(rootId);}//通过递归的方式组装树形结构（层级过多时占用内存较大，数据不规范时有内存溢出风险）public static <T,K,R> List<R> list2tree(List<T> list,K rootId,Function<T,K> idGetter,Function<T,K> pidGetter,Function<T,R> converter,BiConsumer<R,List<R>> childrenSetter){return list.stream().filter(t -> {K parentId = pidGetter.apply(t);return Objects.equals(parentId, rootId);}).map(t -> {K id = idGetter.apply(t);R node = converter.apply(t);List<R> children = list2tree(list, id, idGetter, pidGetter, converter, childrenSetter);if(!children.isEmpty()){childrenSetter.accept(node, children);}return node;}).collect(Collectors.toList());}//通过Map+实现接口的方式组装树形结构public static <T,K> List<TreeNode<K>> list2tree(List<T> list,K rootId,Function<T,TreeNode<K>> converter,Supplier<TreeNode<K>> builder){Map<K, TreeNode<K>> map = new HashMap<>();for (T t : list) {TreeNode<K> node = converter.apply(t);K id = node.getId(), parentId = node.getParentId();//查找当前节点TreeNode<K> currNode = map.get(id);if(currNode != null){//当前节点已存在（被其他节点以父节点加入）//复制子节点集合node.setChildren(currNode.getChildren());}map.put(id, node);//更新或添加当前节点//查找父节点TreeNode<K> parentNode = map.get(parentId);if(parentNode == null){//父节点不存在，则创建父节点，并将自身添加到父节点的子节点集合中parentNode = builder.get();parentNode.addChild(node);map.put(parentId, parentNode);}else{//父节点已存在，直接将自身添加到父节点的子节点集合中parentNode.addChild(node);}}TreeNode<K> rootNode = map.get(rootId);return rootNode==null ? Collections.emptyList() : rootNode.getChildren();}//通过递归+实现接口的方式组装树形结构public static <T,K> List<TreeNode<K>> list2tree(List<T> list,K rootId,Function<T,TreeNode<K>> converter){return list.stream().map(converter).filter(node -> {K parentId = node.getParentId();return Objects.equals(parentId, rootId);}).peek(node -> {K id = node.getId();List<TreeNode<K>> children = list2tree(list, id, converter);if(!children.isEmpty()){node.setChildren(children);}}).collect(Collectors.toList());}private static final Map<String,Field[]> fieldsCache = new HashMap<>();private static String[] getNullProperties(Object obj) {Class<?> clazz = obj.getClass();String className = clazz.getName();Field[] fields = fieldsCache.get(className);if(fields == null){fields = clazz.getDeclaredFields();Field.setAccessible(fields, true);fieldsCache.put(className, fields);}List<String> nullProperties = new ArrayList<>();for (Field field : fields) {try {Object value = field.get(obj);if (value == null) {nullProperties.add(field.getName());}} catch (IllegalAccessException e) {e.printStackTrace();}}String[] result = new String[nullProperties.size()];return nullProperties.toArray(result);}
}

二、接口定义

定义节点规范

package com.server.utils.tree;import java.util.List;/*** @author visy.wang* @date 2024/7/1 10:45*/
public interface TreeNode<K> {K getId();K getParentId();void addChild(TreeNode<K> child);List<TreeNode<K>> getChildren();void setChildren(List<TreeNode<K>> children);
}

三、原始对象

package com.server.utils.tree;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.io.Serializable;/*** 菜单*/
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Menu implements Serializable {private static final long serialVersionUID = 1L;/*** 菜单id*/private Long id;/*** 父id*/private Long fid;/*** 机构名称*/private String name;/*** 模块id*/private Integer level;/*** 状态   1 启用 2 停用*/private Integer status;/*** 权重*/private Integer weight;
}

四、节点对象

package com.server.utils.tree;import lombok.Data;
import lombok.EqualsAndHashCode;import java.util.ArrayList;
import java.util.List;/*** @author visy.wang* @date 2024/6/27 21:54*/
@Data
@EqualsAndHashCode(callSuper = true)
public class MenuNode extends Menu { //不一定要继承原始对象（字段都能复用的时候才考虑继承）/*** 是否勾选*/private Integer isCheck;/*** 子菜单列表*/private List<MenuNode> children;public void addChild(MenuNode child){if(children == null){children = new ArrayList<>();}children.add(child);}
}

五、测试

package com.server.utils.tree;import com.alibaba.fastjson.JSON;
import org.springframework.beans.BeanUtils;import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;/*** @author visy.wang* @date 2024/6/27 21:55*/
public class Test {public static void main(String[] args) {List<Menu> menuList = new ArrayList<>();//顺序可以任意调整，不影响结果menuList.add(new Menu(1L, null, "菜单A", 1, 1,1));menuList.add(new Menu(4L, 2L, "菜单BA", 2, 1,4));menuList.add(new Menu(3L, 1L, "菜单AA", 2, 1,3));menuList.add(new Menu(5L, 3L, "菜单AAA", 3, 1,5));menuList.add(new Menu(2L, null, "菜单B", 1, 1,2));//勾选的菜单ID集合Set<Long> checkedMenuIds = new HashSet<>();checkedMenuIds.add(3L);checkedMenuIds.add(5L);//map的方式MenuNode root = TreeUtil.list2tree(menuList, //原始列表null, //根节点ID，用于提取顶层节点Menu::getId, //获取ID的方法，也可以指定别的字段Menu::getFid, //获取父ID的方法，也可以指定别的字段，但是必须和上面的方法对应menu -> { //将列表中的原始对象转换成节点对象（一般来说比原始对象多了对子节点集合的持有，除此之外也可以按需要增减字段）MenuNode node = new MenuNode();//创建一个节点BeanUtils.copyProperties(menu, node);//复制原始对象的字段到节点对象node.setIsCheck(checkedMenuIds.contains(menu.getId()) ? 1 : 0);//单独设置其他字段return node;//返回节点对象},MenuNode::new, //节点对象的构造方法，用于创建一个新的父节点对象MenuNode::addChild //添加子节点的方法);System.out.println(JSON.toJSONString(root.getChildren()));//递归的方式List<MenuNode> menuNodeList = TreeUtil.list2tree(menuList, //原始列表null, //根节点IDMenu::getId, //获取ID的方法，也可以指定别的字段Menu::getFid, //获取父ID的方法，也可以指定别的字段，但是必须和上面的方法对应menu -> { //将列表中的原始对象转换成节点对象（一般来说比原始对象多了对子节点集合的持有，除此之外也可以按需要增减字段）MenuNode node = new MenuNode();//创建一个节点BeanUtils.copyProperties(menu, node);//复制原始对象的字段到节点对象node.setIsCheck(checkedMenuIds.contains(menu.getId()) ? 1 : 0);//单独设置其他字段return node;//返回节点对象},MenuNode::setChildren //设置子节点集合的方法);System.out.println(JSON.toJSONString(menuNodeList));}
}

六、打印结果

map的方式：

[{"children": [{"children": [{"fid": 3, "id": 5, "isCheck": 1, "level": 3, "name": "菜单AAA", "status": 1, "weight": 5}], "fid": 1, "id": 3, "isCheck": 1, "level": 2, "name": "菜单AA", "status": 1, "weight": 3}], "id": 1, "isCheck": 0, "level": 1, "name": "菜单A", "status": 1, "weight": 1}, {"children": [{"fid": 2, "id": 4, "isCheck": 0, "level": 2, "name": "菜单BA", "status": 1, "weight": 4}], "id": 2, "isCheck": 0, "level": 1, "name": "菜单B", "status": 1, "weight": 2}
]

递归的方式：

[{"children": [{"children": [{"fid": 3, "id": 5, "isCheck": 1, "level": 3, "name": "菜单AAA", "status": 1, "weight": 5}], "fid": 1, "id": 3, "isCheck": 1, "level": 2, "name": "菜单AA", "status": 1, "weight": 3}], "id": 1, "isCheck": 0, "level": 1, "name": "菜单A", "status": 1, "weight": 1}, {"children": [{"fid": 2, "id": 4, "isCheck": 0, "level": 2, "name": "菜单BA", "status": 1, "weight": 4}], "id": 2, "isCheck": 0, "level": 1, "name": "菜单B", "status": 1, "weight": 2}
]

七、实现接口的方式

节点对象

节点对象必须实现TreeNode接口，泛型中指定子父关联字段的类型

package com.server.utils.tree;import lombok.Data;
import lombok.EqualsAndHashCode;import java.util.ArrayList;
import java.util.List;/*** @author visy.wang* @date 2024/7/1 11:31*/
@Data
@EqualsAndHashCode(callSuper = true)
public class MenuNodeV2 extends Menu implements TreeNode<Long>{/*** 是否勾选*/private Integer isCheck;/*** 子菜单列表*/private List<TreeNode<Long>> children;@Overridepublic Long getParentId() {return getFid();}@Overridepublic void addChild(TreeNode<Long> child) {if(this.children == null){this.children = new ArrayList<>();}this.children.add(child);}
}

测试

package com.server.utils.tree;import com.alibaba.fastjson.JSON;
import org.springframework.beans.BeanUtils;import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;/*** @author visy.wang* @date 2024/6/27 21:55*/
public class Test {public static void main(String[] args) {List<Menu> menuList = new ArrayList<>();//顺序可以任意调整，不影响结果menuList.add(new Menu(1L, null, "菜单A", 1, 1,1));menuList.add(new Menu(4L, 2L, "菜单BA", 2, 1,4));menuList.add(new Menu(3L, 1L, "菜单AA", 2, 1,3));menuList.add(new Menu(5L, 3L, "菜单AAA", 3, 1,5));menuList.add(new Menu(2L, null, "菜单B", 1, 1,2));//勾选的菜单ID集合Set<Long> checkedMenuIds = new HashSet<>();checkedMenuIds.add(3L);checkedMenuIds.add(5L);//map的方式+接口实现List<TreeNode<Long>> treeNodeList = TreeUtil.list2tree(menuList, //原始列表null, //根节点ID，用于提取顶层节点menu -> { //将列表中的原始对象MenuNodeV2 node = new MenuNodeV2();//创建一个节点BeanUtils.copyProperties(menu, node);//复制原始对象的字段到节点对象node.setIsCheck(checkedMenuIds.contains(menu.getId()) ? 1 : 0);//单独设置其他字段return node;//返回节点对象},MenuNodeV2::new);System.out.println(JSON.toJSONString(treeNodeList));//递归的方式+接口实现List<TreeNode<Long>> treeNodeList2 = TreeUtil.list2tree(menuList, //原始列表null, //根节点ID，用于提取顶层节点menu -> { //将列表中的原始对象MenuNodeV2 node = new MenuNodeV2();//创建一个节点BeanUtils.copyProperties(menu, node);//复制原始对象的字段到节点对象node.setIsCheck(checkedMenuIds.contains(menu.getId()) ? 1 : 0);//单独设置其他字段return node;//返回节点对象});System.out.println(JSON.toJSONString(treeNodeList2));}
}

打印结果

map的方式+接口实现

[{"children": [{"children": [{"fid": 3, "id": 5, "isCheck": 1, "level": 3, "name": "菜单AAA", "parentId": 3, "status": 1, "weight": 5}], "fid": 1, "id": 3, "isCheck": 1, "level": 2, "name": "菜单AA", "parentId": 1, "status": 1, "weight": 3}], "id": 1, "isCheck": 0, "level": 1, "name": "菜单A", "status": 1, "weight": 1}, {"children": [{"fid": 2, "id": 4, "isCheck": 0, "level": 2, "name": "菜单BA", "parentId": 2, "status": 1, "weight": 4}], "id": 2, "isCheck": 0, "level": 1, "name": "菜单B", "status": 1, "weight": 2}
]

递归的方式+接口实现

[{"children": [{"children": [{"fid": 3, "id": 5, "isCheck": 1, "level": 3, "name": "菜单AAA", "parentId": 3, "status": 1, "weight": 5}], "fid": 1, "id": 3, "isCheck": 1, "level": 2, "name": "菜单AA", "parentId": 1, "status": 1, "weight": 3}], "id": 1, "isCheck": 0, "level": 1, "name": "菜单A", "status": 1, "weight": 1}, {"children": [{"fid": 2, "id": 4, "isCheck": 0, "level": 2, "name": "菜单BA", "parentId": 2, "status": 1, "weight": 4}], "id": 2, "isCheck": 0, "level": 1, "name": "菜单B", "status": 1, "weight": 2}
]

八、递归方式的优化

public static <T,K,R> List<R> list2tree(List<T> list,K rootId,Function<T,K> idGetter,Function<T,K> pidGetter,Function<T,R> converter,BiConsumer<R,List<R>> childrenSetter){if(Objects.isNull(list) || list.isEmpty()){return null;}List<T> childList = new ArrayList<>(), surplusList = new ArrayList<>();for (T t : list) {if(Objects.equals(rootId, pidGetter.apply(t))){childList.add(t);}else{surplusList.add(t);}}if(childList.isEmpty()){return null;}return childList.stream().map(t -> {K id = idGetter.apply(t);R node = converter.apply(t);List<R> children = list2tree(surplusList, id, idGetter, pidGetter, converter, childrenSetter);childrenSetter.accept(node, children);return node;}).collect(Collectors.toList());
}

public static <T,K> List<TreeNode<K>> list2tree(List<T> list,K rootId,Function<T,TreeNode<K>> converter){if(Objects.isNull(list) || list.isEmpty()){return null;}List<T> surplusList = new ArrayList<>();//剩余列表（将已查找到的节点排除）List<TreeNode<K>> childList = new ArrayList<>();//rootId下的子节点列表for (T t : list) {TreeNode<K> node = converter.apply(t);if(Objects.equals(rootId, node.getParentId())){childList.add(node);}else{surplusList.add(t);}}childList.forEach(node -> {node.setChildren(list2tree(surplusList, node.getId(), converter));});return childList.isEmpty() ? null : childList;
}