java转树形结构工具类详解

本文实例为大家分享了java转树形结构工具类的具体代码，供大家参考，具体内容如下

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import com.alibaba.fastjson.JSON;

import lombok.Data;

import lombok.ToString;

import org.springframework.util.ReflectionUtils;

import org.springframework.util.StringUtils;

import java.lang.reflect.Field;

import java.util.*;

/**

* @author : liyk

* @version 1.0

* @date : 2020/6/9

*/

public class TreeUtil {

/**

* 将 List 转为树形结构

*

* @param origList : 要转换的 List

* @param idFieldName : id字段名

* @param parentIdFieldName : parentId 字段名

* @param childrenFieldName : children 字段名

* @param <T> : 拥有父子结构的 Entity

* @return : 树形结果

* @throws Exception .

*/

public static <T> List<T> convert(List<T> origList, String idFieldName,

String parentIdFieldName, String childrenFieldName) throws Exception {

// 用于保存当前 id 索引的实体类

Map<String, T> idMaps = new HashMap<>();

// 暂存区, 用于保存没有找到父 id 的控件

List<T> tempList = new ArrayList<>();

List<T> result = new ArrayList<>();

for (T entity : origList) {

// 获取 id, parentId, children

String id = Objects.toString(getFieldValue(entity, idFieldName), "");

String parentId = Objects.toString(getFieldValue(entity, parentIdFieldName), "");

if (StringUtils.isEmpty(id)) {

throw new Exception("存在id为空的资料");

}

idMaps.put(id, entity);

if (StringUtils.isEmpty(parentId)) {

// 如果父 id 为空, 则实体类为第一层

result.add(entity);

} else {

// 根据父 id 获取实体类

T parentEntity = idMaps.get(parentId);

if (parentEntity == null) {

// 没找到先放入暂存区

tempList.add(entity);

} else {

// 父组件判断是否存在 children, 不存在新增, 存在则直接假如

setChildrenValue(childrenFieldName, entity, parentEntity);

}

// 处理暂存区, 暂存区的一定不为根节点, 所以它只要父节点存在, 那么此轮查询一定能找到父节点(上一轮已经将全部节点放入 idMaps)

for (T entity : tempList) {

// 获取 parentId

String parentId = Objects.toString(getFieldValue(entity, parentIdFieldName), "");

// 根据父id获取实体类

T parentEntity = idMaps.get(parentId);

if (parentEntity == null) {

throw new Exception("存在孤立的子节点");

} else {

// 父组件判断是否存在children, 不存在新增, 存在则直接假如

setChildrenValue(childrenFieldName, entity, parentEntity);

}

return result;

}

private static <T> void setChildrenValue(String childrenFieldName, T entity, T parentEntity) throws Exception {

Object children = getFieldValue(parentEntity, childrenFieldName);

List<T> childrenList;

if (children == null) {

childrenList = new ArrayList<>();

childrenList.add(entity);

setFieldValue(parentEntity, childrenFieldName, childrenList);

} else {

List<T> childrenReal = (List<T>) children;

childrenReal.add(entity);

}

private static <T> Object getFieldValue(T entity, String fieldName) throws Exception {

Field field = ReflectionUtils.findField(entity.getClass(), fieldName);

if (field == null) {

throw new Exception(String.format("字段名称[%s]不存在", fieldName));

}

boolean accessible = field.isAccessible();

field.setAccessible(true);

Object result = ReflectionUtils.getField(field, entity);

field.setAccessible(accessible);

return result;

}

private static <T> void setFieldValue(T entity, String fieldName, Object value) throws Exception {

Field field = ReflectionUtils.findField(entity.getClass(), fieldName);

if (field == null) {

throw new Exception(String.format("字段名称[%s]不存在", fieldName));

}

boolean accessible = field.isAccessible();

field.setAccessible(true);

ReflectionUtils.setField(field, entity, value);

field.setAccessible(accessible);

}

public static void main(String[] args) throws Exception {

List<Demo> list = new ArrayList<>();

for (int i = 0; i < 5; i++) {

Demo demo = new Demo(i, "一级节点" + i);

list.add(demo);

}

for (int i = 5; i < 15; i++) {

Demo demo = new Demo(i, i % 5, "二级节点" + i);

list.add(demo);

}

for (int i = 15; i < 100; i++) {

Demo demo = new Demo(i, i % 10 + 5, "三级节点" + i);

list.add(demo);

}

Demo demo = new Demo(100, 102, "非法节点");

list.add(demo);

List<Demo> convert = TreeUtil.convert(list, "id", "pid", "children");

String s = JSON.toJSONString(convert);

System.out.println(s);

}

@Data

@ToString

class Demo {

private Integer id;

private Integer pid;

private String name;

private List<Demo> children;

public Demo(Integer id, Integer pid, String name) {

this.id = id;

this.pid = pid;

this.name = name;

}

public Demo(Integer id, String name) {

this.id = id;

this.name = name;

}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持快网idc。

原文链接：https://blog.csdn.net/l707268743/article/details/106642018

java转树形结构工具类详解

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