基于Lamada表达式的树结构遍历

最近在做项目中需要做部门树的生成, 之前我们有两种方法,一种是mysql中写存储过程用递归的方法生成,另一种是java中用for循环递归的方式,最近在网上看到大神有用Lamada表达式的方法,觉得这样写很简洁很直观,基于我们的需求所以写了一个demo,有不对的地方,望大神指正.

package com.yihur.demo;

import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import org.junit.Before;
import org.junit.Test;

import java.util.*;

/**
 * @author yihur
 * @description 树结构遍历---已知子节点遍历子节点的所有叶子节点
 * @date 2019/4/1
 */
public class TreeTestDemo {

    private List<Map<String,Object>> bodyList;

    private List<Map<String,Object>> rootList;

    //用于存放该节点下所有节点,
    private List<Map<String,Object>> beanList;

    @Before
    public void before_new_list(){
        bodyList = new ArrayList<>();
        rootList = new ArrayList<>();
        beanList = new ArrayList<>();
    }

    /**
     * 所有节点
     * @author yihur
     * @date 2019/4/4
     * @param
     * @return java.util.List<java.util.Map<java.lang.String,java.lang.Object>>
     */
    private List<Map<String,Object>> selectAllTreeNode(){
        List<Map<String,Object>> resultReturn= new ArrayList<>();
        Map<String,Object> map = new HashMap<>();

        map.put("id","100");
        map.put("parentID","10");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","200");
        map.put("parentID","100");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","201");
        map.put("parentID","100");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","300");
        map.put("parentID","200");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","301");
        map.put("parentID","201");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","400");
        map.put("parentID","300");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","401");
        map.put("parentID","301");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","500");
        map.put("parentID","400");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","501");
        map.put("parentID","401");
        resultReturn.add(map);

        return resultReturn;
    }

    /**
     * 根节点 或 起始节点
     * @author yihur
     * @date 2019/4/4
     * @param
     * @return java.util.List<java.util.Map<java.lang.String,java.lang.Object>>
     */
    private List<Map<String,Object>> selectRootTreeNode(){
        List<Map<String,Object>> resultReturn= new ArrayList<>();
        Map<String,Object> map = new HashMap<>();

        map.put("id","100");
        map.put("parentID","10");
        resultReturn.add(map);
        map = new HashMap<>();

        map.put("id","200");
        map.put("parentID","100");
        resultReturn.add(map);

        return resultReturn;
    }


    @Test
    public void test_tree_node_by_current_node(){
        List<Map<String,Object>> rootList = selectRootTreeNode();
        bodyList = selectAllTreeNode();
        // newHashMapWithExpectedSize是guava中的方法,用于初始化一个特定大小的HashMap
        Map<String, String> map = Maps.newHashMapWithExpectedSize(bodyList.size());
        rootList.forEach(beanTree -> getChild(beanTree, map));

        System.out.println(Arrays.toString(rootList.toArray()));
        beanList.addAll(rootList);
        System.out.println(Arrays.toString(beanList.toArray()));
        System.out.println(Arrays.toString(bodyList.toArray()));
    }

    /**
     * 方法描述
     * @author yihur
     * @date 2019/4/4
     * @param beanTree
     * @param map
     * @return void
     */
    private void getChild(Map<String, Object> beanTree ,Map<String, String> map) {
        List<Map<String,Object>> childList = Lists.newArrayList();
        bodyList.stream()
                .filter(c -> !map.containsKey(c.get("id").toString()))
                .filter(c -> c.get("parentID").toString().equals(beanTree.get("id").toString()))
                .forEach(c -> {
                    map.put(c.get("id").toString(), c.get("parentID").toString());
                    getChild(c, map);
                    childList.add(c);
                });
        // 所有叶子结点不加childList参数,避免叶子节点带有该参数下,前端控件依然显示加号
        if (childList.size() != 0) {
            beanTree.put("childList",childList);
            beanList.addAll(childList);
        }
    }


}