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目录前言一、树形结构是什么?二、实现方案1、stream流递归实现1.1 实体类1.2 实现类2、jdk1.7以下实现2.1 节点类2.2 实现类3、应用场景3.1 用于前端方便展示
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
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。
public class TreeBean {
private Integer id;
private String name;
public Integer parentId;
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;
}
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;
}
}
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));
}
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;
}
便于提供前端取值
以删除菜单做例子,一般菜单未免会带子菜单,所以,“父找子” 需求应声而来;
代码如下:
资料参考:
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