java中把一个list转tree的三种方法——工具类

java中把一个list转tree的三种实现方法

如何使用：

如果你的类中主键名称为id，父节点id名称为parentId，子节点列表名称为children，数据库中顶层父节点id值为“0”，可以直接调用只需传入需要转换list的方法。否则需要传入相应的字段名称，或者修改代码。

import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.lang3.StringUtils;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;


/**
 * @author :Kite
 * @Date : 2023/5/8 9:52
 */
public class TreeUtil {

    /**
     * 通过递归方式构建树
     *
     * @param list 列表
     * @return {@link List}
     */
    public static  List buildTreeByRecursion(List list) {
        return buildTreeByRecursion(list, "id", "parentId", "children");
    }

    /**
     * 通过Map方式构建树
     *
     * @param list 列表
     * @return {@link List}
     */
    public static  List buildTreeByMap(List list) {
        return buildTreeByMap(list, "id", "parentId", "children", "0");
    }

    /**
     * 通过两层for循环方式构建树
     *
     * @param list 列表
     * @return {@link List}
     */
    public static  List buildTreeByTwoLayersFor(List list) {
        return buildTreeByTwoLayersFor(list, "id", "parentId", "children", "0");
    }

    /**
     * 通过递归方式构建树
     *
     * @param list         列表
     * @param idName       id名称
     * @param parentIdName 父id名称
     * @param childrenName 子节点列表名称
     * @return {@link List}
     */
    public static  List buildTreeByRecursion(List list, String idName, String parentIdName, String childrenName) {
        if (StringUtils.isBlank(idName) || StringUtils.isBlank(parentIdName) || StringUtils.isBlank(childrenName)) {
            return new ArrayList();
        }
        List returnList = new ArrayList();
        //获取list中所有的主键id
        List ids = list.stream().map(o -> getFieldValue(o, idName).toString()).toList();

        for (T t : list) {
            String parentId = getFieldValue(t, parentIdName).toString();
            //如果是顶级节点, 遍历该父节点的所有子节点,因为顶层的parentId为0
            if (!ids.contains(parentId)) {
                buildTreeRecursive(list, t, idName, parentIdName, childrenName);
                returnList.add(t);
            }
        }
        if (returnList.isEmpty()) {
            returnList = list;
        }
        return returnList;
    }

    /**
     * 递归fn
     *
     * @param list 分类表
     * @param node 子节点
     */
    private static  void buildTreeRecursive(List list, T node, String idName, String parentIdName, String childrenName) {
        // 得到子节点列表
        List childList = getChildList(list, node, idName, parentIdName);
        setFieldValue(node, childList, childrenName);
        for (T child : childList) {
            if (hasChild(list, child, idName, parentIdName)) {
                buildTreeRecursive(list, child, idName, parentIdName, childrenName);
            }
        }
    }

    /**
     * 得到子节点列表
     */
    private static  List getChildList(List list, T node, String idName, String parentIdName) {
        List tlist = new ArrayList();
        String oId = getFieldValue(node, idName).toString();
        for (T child : list) {
            String tParentId = getFieldValue(child, parentIdName).toString();
            if (tParentId.equals(oId)) {
                tlist.add(child);
            }
        }
        return tlist;
    }

    /**
     * 判断是否有子节点
     */
    private static  boolean hasChild(List list, T t, String idName, String parentIdName) {
        return getChildList(list, t, idName, parentIdName).size() > 0;
    }

    /**
     * 通过Map方式构建树
     *
     * @param list           列表
     * @param idName         id名称
     * @param parentIdName   父id名称
     * @param childrenName   子节点列表名称
     * @param topParentIdVal 顶层节点父id的值
     * @return {@link List}
     */
    public static  List buildTreeByMap(List list, String idName, String parentIdName, String childrenName, String topParentIdVal) {
        if (StringUtils.isBlank(idName) || StringUtils.isBlank(parentIdName) || StringUtils.isBlank(childrenName)) {
            return new ArrayList();
        }
        //根据parentId进行分组
        Map<String, List> mapList = list.stream().collect(Collectors.groupingBy(o -> getFieldValue(o, parentIdName).toString()));
        //给每个节点设置子节点列表
        list.forEach(node -> setFieldValue(node, mapList.get(getFieldValue(node, idName).toString()), childrenName));
        return list.stream().filter(o -> topParentIdVal.equals(getFieldValue(o, parentIdName))).collect(Collectors.toList());
    }

    /**
     * 获取属性值
     *
     * @param o         对象
     * @param fieldName 属性名
     * @return {@link String}
     */
    private static Object getFieldValue(Object o, String fieldName) {
        try {
            Class oClass = o.getClass();
            Field field = oClass.getDeclaredField(fieldName);
            field.setAccessible(true);
            return field.get(o);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * 设置字段值
     *
     * @param o         对象
     * @param val       值
     * @param fieldName 属性名
     */
    private static void setFieldValue(Object o, Object val, String fieldName) {
        try {
            Class oClass = o.getClass();
            Field field = oClass.getDeclaredField(fieldName);
            field.setAccessible(true);
            field.set(o, val);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * 通过两层for循环方式构建树
     *
     * @param list           列表
     * @param idName         id名称
     * @param parentIdName   父id名称
     * @param childrenName   子节点列表名称
     * @param topParentIdVal 顶层节点父id的值
     * @return {@link List}
     */
    public static  List buildTreeByTwoLayersFor(List list, String idName, String parentIdName, String childrenName, String topParentIdVal) {
        List resultList = new ArrayList();
        for (T node : list) {
            //如果是顶层节点
            if (topParentIdVal.equals(getFieldValue(node, parentIdName))) {
                resultList.add(node);
            }
            for (T child : list) {
                if (getFieldValue(child, parentIdName).equals(getFieldValue(node, idName))) {
                    List childrenList = (List) getFieldValue(node, childrenName);
                    if (CollectionUtils.isEmpty(childrenList)) {
                        childrenList = new ArrayList();
                        setFieldValue(node, childrenList, childrenName);
                    }
                    childrenList.add(child);
                }
            }
        }
        return resultList;
    }

}