前言

本文提供两种递归实现思路
树形结构数据，大体的实现思路就是“父找子”，父节点去层层递归寻找子节点，最后组装成数据集合。

提示：以下是本篇文章正文内容，下面案例可供参考

一、树形结构是什么？

树形结构，和我们平常所触及到的无限级菜单，是同一个道理。
所谓树形结构，我们可以将其理解为:树根或者树冠，都可以无限分叉下去。
现有一张表，需要对表中数据进行分级查询(按照上下级关系进行排列)，我们常用的数据库有: oracle和mysql;
如果使用oracle的话，使用connect by，很容易就能做到;
但是，mysql没有现成的递归函数，需要我们自己使用存储过程封装，而且，就算封装好了递归函数，mysql在执行的时候，查询速度会很慢。如何解决这个问题呢?
既然数据库不给力，我们只能交由程序来处理了，以减轻mysql数据库的压力。

二、实现方案

1、stream流递归实现

1.1 实体类

public class TreeBean {
    
    
 
    /**
     * id
     */
    private Integer id;
 
    /**
     * 名称
     */
    private String name;
 
    /**
     * 父id ，根节点为0
     */
    public Integer parentId;
 
    /**
     * 子节点信息
     */
    public List<TreeBean> childList;
 
    public TreeBean() {
    
    
    }
 
    public TreeBean(Integer id, String name, Integer parentId, List<TreeBean> childList) {
    
    
        this.id = id;
        this.name = name;
        this.parentId = parentId;
        this.childList = childList;
    }
 
    public Integer getId() {
    
    
        return id;
    }
 
    public void setId(Integer id) {
    
    
        this.id = id;
    }
 
    public String getName() {
    
    
        return name;
    }
 
    public void setName(String name) {
    
    
        this.name = name;
    }
 
    public Integer getParentId() {
    
    
        return parentId;
    }
 
    public void setParentId(Integer parentId) {
    
    
        this.parentId = parentId;
    }
 
    public List<TreeBean> getChildList() {
    
    
        return childList;
    }
 
    public void setChildList(List<TreeBean> childList) {
    
    
        this.childList = childList;
    }
 
    /**
     * 初始化数据
     * @return
     */
    public List<TreeBean> initializationData() {
    
    
        List<TreeBean> list = new ArrayList<>();
        TreeBean t1 = new TreeBean(1, "广东省", 0, new ArrayList<>());
        TreeBean t2 = new TreeBean(2, "湖南省", 0, new ArrayList<>());
        TreeBean t3 = new TreeBean(3, "广州市", 1, new ArrayList<>());
        TreeBean t4 = new TreeBean(4, "长沙市", 2, new ArrayList<>());
        TreeBean t5 = new TreeBean(5, "白云区", 3, new ArrayList<>());
        TreeBean t6 = new TreeBean(6, "黄浦区", 3, new ArrayList<>());
        TreeBean t7 = new TreeBean(7, "白云街道", 5, new ArrayList<>());
        TreeBean t8 = new TreeBean(8, "深圳市", 1, new ArrayList<>());
        TreeBean t9 = new TreeBean(9, "宝安区", 8, new ArrayList<>());
        TreeBean t10 = new TreeBean(10, "福田区", 8, new ArrayList<>());
        TreeBean t11 = new TreeBean(11, "南山区", 8, new ArrayList<>());
        TreeBean t12 = new TreeBean(12, "南山街道", 11, new ArrayList<>());
        TreeBean t13 = new TreeBean(13, "芙蓉区", 4, new ArrayList<>());
        TreeBean t14 = new TreeBean(14, "岳麓区", 4, new ArrayList<>());
        TreeBean t15 = new TreeBean(15, "开福区", 4, new ArrayList<>());
        TreeBean t16 = new TreeBean(16, "岳阳市", 2, new ArrayList<>());
        TreeBean t17 = new TreeBean(17, "岳麓街道", 14, new ArrayList<>());
        list.add(t1);
        list.add(t2);
        list.add(t3);
        list.add(t4);
        list.add(t5);
        list.add(t6);
        list.add(t7);
        list.add(t8);
        list.add(t9);
        list.add(t10);
        list.add(t11);
        list.add(t12);
        list.add(t13);
        list.add(t14);
        list.add(t15);
        list.add(t16);
        list.add(t17);
        return list;
    }
 
 
}

1.2 实现类

/**
     * 方式一：Stream流递归实现遍历树形结构
     */
    public static void treeTest1() {
    
    
        //获取数据
        List<TreeBean> treeBeans = new TreeBean().initializationData();
        //获取父节点
        List<TreeBean> collect = treeBeans.stream().filter(t -> t.getParentId() == 0).map(
                m -> {
    
    
                    m.setChildList(getChildren(m, treeBeans));
                    return m;
                }
        ).collect(Collectors.toList());
        System.out.println(JSON.toJSONString(collect));
    }

    /**
     * 递归查询子节点
     * @param root  根节点
     * @param all   所有节点
     * @return 根节点信息
     */
    public static List<TreeBean> getChildren(TreeBean root, List<TreeBean> all) {
    
    
        List<TreeBean> children = all.stream().filter(t -> {
    
    
            return Objects.equals(t.getParentId(), root.getId());
        }).map(
                m -> {
    
    
                    m.setChildList(getChildren(m, all));
                    return m;
                }
        ).collect(Collectors.toList());
        return children;
    }