Java集合List转树结构工具类-函数版

￡神魔★判官ぃ 2023-01-13 05:46 163阅读 0赞

*  工具类:

package com.example.mindsa.util.tree;
    
    import com.baomidou.mybatisplus.core.toolkit.support.SFunction;
    import lombok.SneakyThrows;
    
    import java.lang.invoke.SerializedLambda;
    import java.lang.reflect.Method;
    import java.util.List;
    import java.util.function.Function;
    import java.util.stream.Collectors;
    
    /**
     * 树形工具类-函数版
     *
     * @author sunziwen
     */
    
    public class TreeUtil {
        /**
         * @param list          树结构的基础数据集
         * @param getIdFn       获取主键的函数
         * @param getParentIdFn 获取父节点的函数
         * @param getChildrenFn 获取子集的函数
         * @param <T>           t
         * @param <R>           r
         * @return t
         */
        @SneakyThrows
        public static <T, R> List<T> treeOut(List<T> list, Function<T, R> getIdFn, Function<T, R> getParentIdFn, SFunction<T, R> getChildrenFn) {
            /*所有元素的Id*/
            List<Object> ids = list.stream().map(getIdFn).collect(Collectors.toList());
            /*查出所有顶级节点*/
            List<T> topLevel = list.stream().filter(x -> {
                R apply = getParentIdFn.apply(x);
                return !ids.contains(apply);
            }).collect(Collectors.toList());
            return TreeUtil.recursion(topLevel, list, getIdFn, getParentIdFn, getChildrenFn);
        }
    
    
        @SneakyThrows
        private static <T, R> List<T> recursion(List<T> superLevel, List<T> list, Function<T, R> getIdFn, Function<T, R> getParentIdFn, SFunction<T, R> getChildrenFn) {
            //获取setChildren的Method
            Method writeReplaceMethod = getChildrenFn.getClass().getDeclaredMethod("writeReplace");
            boolean accessible = writeReplaceMethod.isAccessible();
            writeReplaceMethod.setAccessible(true);
            SerializedLambda serializedLambda = (SerializedLambda) writeReplaceMethod.invoke(getChildrenFn);
            writeReplaceMethod.setAccessible(accessible);
            String setMethodName = serializedLambda.getImplMethodName().replaceFirst("g", "s");
            Method setMethod = Class.forName(serializedLambda.getImplClass().replace("/", ".")).getDeclaredMethod(setMethodName, List.class);
    
            for (T t : superLevel) {
                List<T> children = list.stream().filter(x -> {
                    R apply = getParentIdFn.apply(x);
                    R apply1 = getIdFn.apply(t);
                    return apply.equals(apply1);
                }).collect(Collectors.toList());
                if (children.size() <= 0) {
                    continue;
                }
    
                List<T> recursion = recursion(children, list, getIdFn, getParentIdFn, getChildrenFn);
                setMethod.invoke(t, recursion);
            }
            return superLevel;
        }
    
    
    }

*  使用示例:

public static void main(String[] args) {
            //模拟数据
            ArrayList<My> list = new ArrayList<My>() {
       {
                add(new My("1", "-1", "a"));
                add(new My("2", "-1", "aa"));
                add(new My("3", "1", "b"));
                add(new My("4", "1", "c"));
                add(new My("5", "3", "d"));
                add(new My("6", "5", "e"));
                add(new My("7", "6", "f"));
                add(new My("8", "2", "g"));
                add(new My("9", "8", "h"));
                add(new My("10", "9", "i"));
            }};
    
            //使用工具类:
            List<My> result = TreeUtil.treeOut(list, My::getUserid, My::getPId, My::getChs);
            //打印
            System.out.println(JSON.toJSONString(result));
        }

*  大功告成了,如果有问题请加博主V：sunziwen3366