Java通用List转树-函数版-BiConsumer示例

时间：2025-04-02 14:24:45

  • 在网上搜了下list转树，大部分都是递归和两个for循环，无意间发现了这条博客/zhizhao/p/，感觉时间复杂度要好很多，同样的数据量递归和嵌套for循环要用5~6秒，而这种方法只要十毫秒左右（原理是把list转成map，利用map的特点）。但生成的树是json格式，所以就改写成下面这种返回值是list集合的。（一定要看到最后！！！）

  • 要转换的模型：TreeDto


import com.alibaba.fastjson.JSON;
import lombok.Data;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class ListToTreeTest {

    private static List<TreeDto> listToTree(List<TreeDto> oldList) {
        Map<String, Object> newMap = new HashMap<>();
        List<TreeDto> result = new ArrayList<>();
        for (TreeDto treeDto : oldList) {
            newMap.put(treeDto.getId(), treeDto);
        }
        for (TreeDto treeDto : oldList) {
            TreeDto parent = (TreeDto) newMap.get(treeDto.getPid());
            if (parent != null) {
                if (parent.getChildren() == null) {
                    List<TreeDto> ch = new ArrayList<>();
                    ch.add(treeDto);
                    parent.setChildren(ch);
                } else {
                    List<TreeDto> ch = parent.getChildren();
                    ch.add(treeDto);
                    parent.setChildren(ch);
                }
            } else {
                result.add(treeDto);
            }
        }
        return result;
    }

    public static void main(String[] args) {
        List<TreeDto> testTree = new ArrayList<TreeDto>() {{
            add(new TreeDto("1", "0", "第1层", "01"));
            add(new TreeDto("11", "1", "第2层", "0101"));
            add(new TreeDto("12", "1", "第2层", "0102"));
            add(new TreeDto("2", "0", "第1层", "02"));
            add(new TreeDto("3", "4", "第4层", "03"));
            add(new TreeDto("4", "11", "第3层", "010101"));
        }};
        System.out.println(JSON.toJSONString(listToTree(testTree)));
    }

    @Data
    static class TreeDto {

        public TreeDto(String id, String pid, String name, String treeNo) {
            this.id = id;
            this.pid = pid;
            this.name = name;
            this.treeNo = treeNo;
        }

        private String id;
        private String pid;//fatherid
        private String name;
        private String treeNo;
        private List<TreeDto> children;

    }

}
  • 但是改成这样这个方法就不能通用了，然后再改，抽象出id，父id和子集，重写就能用，参考：/magonong/article/details/80179400

1抽象类：


import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public abstract class List2tree<N> {

    /**
     * 主键ID
     *
     * @param node
     * @return
     */
    protected abstract Serializable getKey(N node);

    /**
     * 父节点
     *
     * @param node
     * @return
     */
    protected abstract Serializable getParentId(N node);

    /**
     * 子节点
     *
     * @param node
     * @return
     */
    protected abstract List<N> getChildrens(N node);

    protected abstract void setChildrens(List<N> nodes, N node);

    /**
     * 生成树方法
     *
     * @param oldList
     * @return
     */
    public List<N> listToTree(List<N> oldList) {

        Map<Serializable, N> newMap = oldList.stream().collect(Collectors.toMap(this::getKey, N -> N));

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

        oldList.forEach(tree -> {
            N parent = newMap.get(getParentId(tree));
            if (parent == null) {
                result.add(tree);
            } else {
                List<N> ch = getChildrens(parent);
                if (ch == null) {
                    ch = new ArrayList<>();
                }
                ch.add(tree);
                setChildrens(ch, parent);
            }
        });
        return result;

    }

}

2测试：

import com.alibaba.fastjson.JSON;
import lombok.Data;

import java.util.ArrayList;
import java.util.List;

public class MainTest {

    public static void main(String[] args) {
        //重写
        List2tree<TreeDto> list2tree2 = new List2tree<TreeDto>() {
            @Override
            public String getKey(TreeDto node) {
                return node.getId();
            }

            @Override
            protected String getParentId(TreeDto node) {
                return node.getPid();
            }

            @Override
            protected List<TreeDto> getChildrens(TreeDto node) {
                return node.getChildren();
            }

            @Override
            protected void setChildrens(List<TreeDto> nodes, TreeDto node) {
                node.setChildren(nodes);
            }
        };

        //模拟数据
        List<TreeDto> list = new ArrayList<TreeDto>() {{
            add(new TreeDto("1", "0", "第1层"));
            add(new TreeDto("11", "1", "第2层"));
            add(new TreeDto("12", "1", "第2层"));
            add(new TreeDto("2", "0", "第1层"));
            add(new TreeDto("3", "4", "第4层"));
            add(new TreeDto("4", "11", "第3层"));
        }};
        System.out.println(JSON.toJSONString(list2tree2.listToTree(list)));

    }

    @Data
    static class TreeDto {

        public TreeDto(String id, String pid, String name) {
            this.id = id;
            this.pid = pid;
            this.name = name;
        }

        private String id;
        private String pid;//父id
        private String name;
        private List<TreeDto> children;

    }
}
  • 摸鱼的时候，被我发现了这条博客/wenxingchen/article/details/115749782里面使用了反射，递归并且使用函数实现重写，就模仿他改成了下面的究极无敌最终函数进化版 ！！！
import com.alibaba.fastjson.JSON;
import lombok.Data;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.BiConsumer;
import java.util.function.Function;
import java.util.stream.Collectors;

public class List2tree {

    /**
     * listToTree
     * @param target      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> target, Function<T, R> getId, Function<T, R> getParentId,
                                            Function<T, List<T>> getChildren, BiConsumer<T, List<T>> setChildren) {

        Map<R, T> oldMap = target.stream().collect(Collectors.toMap(getId, T -> T));
        List<T> result = new ArrayList<>();
        target.forEach(tree -> {
            T parent = oldMap.get(getParentId.apply(tree));
            if (parent == null) {
                result.add(tree);
            } else {
                List<T> ch = getChildren.apply(parent);
                if (ch == null) {
                    ch = new ArrayList<>();
                }
                ch.add(tree);
                setChildren.accept(parent, ch);
            }
        });
        return result;
    }


    public static void main(String[] args) {
        //模拟数据
        List<TreeDto> list = new ArrayList<TreeDto>() {{
            add(new TreeDto("1", "0", "第1层"));
            add(new TreeDto("11", "1", "第2层"));
            add(new TreeDto("12", "1", "第2层"));
            add(new TreeDto("2", "0", "第1层"));
            add(new TreeDto("3", "4", "第4层"));
            add(new TreeDto("4", "11", "第3层"));
        }};

        System.out.println(JSON.toJSONString(List2tree.listToTree(list, TreeDto::getId, TreeDto::getPid,
                TreeDto::getChildren, TreeDto::setChildren)));
    }

    @Data
    static class TreeDto {

        public TreeDto(String id, String pid, String name) {
            this.id = id;
            this.pid = pid;
            this.name = name;
        }

        private String id;
        private String pid;//父id
        private String name;
        private List<TreeDto> children;

    }

}
  • 有关 JDK8 | BiConsumer＜T,U＞实践应用 /shichen2010/article/details/108284064

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