list转换成树形结构

import cn.hutool.core.collection.CollectionUtil;
import cn.hutool.core.util.StrUtil;
import cn.hutool.json.JSONUtil;
import com.alibaba.fastjson.JSON;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Hashtable;
import java.util.List;
import java.util.Map;

/**
 * list转换成树形结构
 */
@Component
public class ConvertorUtil<T> {


    public static String PRIMARY_FIELD_NAME = "id";
    public static String PARENT_FIELD_NAME = "pid";
    public static String CHILDREN_LIST = "childrenList";
    public static String PID_VALUE = "0";

    public static String PRIMARY_FIELD_ENDS_WITH= "Pid";
    public static String PARENT_FIELD_ENDS_WITH= "Id";

    /**
     * @param entityList       要转换的数据
     * @param primaryFieldName 主键ID
     * @param parentFieldName  父ID
     * @param childrenName     子集合属性名
     * @param pidValue         顶级父ID值
     * @return 树形结构list
     */
    @SuppressWarnings("unchecked")
    public List<T> listToTree(List<?> entityList, String primaryFieldName, String parentFieldName, String childrenName, String pidValue) {
        if (CollectionUtil.isEmpty(entityList)) {
            return new ArrayList<>();
        }
        Object o = entityList.get(0);
        if (StrUtil.isNotBlank(primaryFieldName) && StrUtil.isNotBlank(parentFieldName)) {
            primaryFieldName = PRIMARY_FIELD_NAME;
            parentFieldName = PARENT_FIELD_NAME;
        } else {
            Class<?> aClass = o.getClass();
            Field[] declaredFields = aClass.getDeclaredFields();
            for (Field field : declaredFields) {
                String name = field.getName();
                if (name.endsWith(PRIMARY_FIELD_ENDS_WITH)) {
                    parentFieldName = name;
                    primaryFieldName = parentFieldName.substring(0, parentFieldName.lastIndexOf(PRIMARY_FIELD_ENDS_WITH)) + PARENT_FIELD_ENDS_WITH;
                }
            }
        }
        if (StrUtil.isBlank(childrenName)) {
            childrenName = CHILDREN_LIST;
        }
        if (StrUtil.isNotBlank(pidValue)) {
            pidValue = PID_VALUE;
        }
        //返回的map Tree树形结构
        List<Map<String, Object>> treeMap = new ArrayList<>();
        //将传进的参数entityList转为MapList
        List<Map<String, Object>> listMap = JSON.parseObject(JSON.toJSONString(entityList), List.class);
        //声明一个map用来存listMap中的对象，key为对象id，value为对象本身
        Map<String, Map<String, Object>> entityMap = new Hashtable<>();
        //循环listMap把map对象put到entityMap中去
        for (Map<String, Object> map : listMap) {
            entityMap.put(map.get(primaryFieldName).toString(), map);
        }
        //循环listMap进行Tree树形结构组装
        for (Map<String, Object> map : listMap) {
            //获取map的pid
            Object pid = map.get(parentFieldName);
            //判断pid是否为空或者为0，为空说明是最顶级，直接add到返回的treeMap中去
            if (pid == null || StrUtil.equals(pid.toString(), pidValue)) {
                treeMap.add(map);
            } else {
                //如果pid不为空也不为0，是子集
                // 根据当前map的pid获取上级 parentMap
                Map<String, Object> parentMap = entityMap.get(pid.toString());
                if (parentMap == null) { //如果parentMap为空，则说明当前map没有父级，当前map就是顶级
                    treeMap.add(map);
                } else {
                    //如果parentMap不为空，则当前map为parentMap的子级
                    //取出parentMap的所有子级的List集合
                    List<Map<String, Object>> children = (List<Map<String, Object>>) parentMap.get(childrenName);
                    if (children == null) {  //判断子级集合是否为空，为空则新创建List
                        children = new ArrayList<>();
                        parentMap.put(childrenName, children);
                    }
                    //把当前map对象add到parentMap的子级List中去
                    children.add(map);
                }
            }
        }
        return JSONUtil.toList(String.valueOf(treeMap), null);
    }


    public List<T> listToTree(List<?> entityList) {
        return listToTree(entityList, "", "", "", "");
    }


    public List<T> listToTree(List<?> entityList, String primaryFieldName, String parentFieldName) {
        return listToTree(entityList, primaryFieldName, parentFieldName, "", "");
    }


    public List<T> listToTree(List<?> entityList, String primaryFieldName, String parentFieldName, String childrenName) {
        return listToTree(entityList, primaryFieldName, parentFieldName, childrenName, "");
    }