1、这回先创建数据库吧
下表cid是CategoryId的缩写,cname是CategoryName的缩写，pid是parentId的缩写
无限级分类一般都包含这三个属性，至少也要包含cid和pid才能建立无限级关联
ok,这个东东就是无限级分类了。
即便是外行人稍微看一眼也能发现cid为1的图书在小说和周刊两行中作为了pid,也就是说小说和周刊的父级分类就是图书
图书和饮料的pid是0，代表他们是顶级分类
如果没有其他约束条件，这张表几乎可以无限向下级延伸，是一个树形结构，这里就不写什么数学公式了，道理很简单。想必大家都懂了。
2、写个实体类
首先还是生产实体类，植入一个他本身的List集合:
1 package cn.sohappy.acourses.bean;
2
3 import java.util.ArrayList;
4 import java.util.List;
5
6 public class Category {
7 private Long cid;
8 private String cname;
9 private Long pid;
10 private List<Category> children;
11
12 //省略getter and setter
13 }
然后初始化children并重写toString方法方便测试，完整代码如下：
1 package cn.sohappy.acourses.bean;
2
3 import java.util.ArrayList;
4 import java.util.List;
5
6 public class Category {
7 private Long cid;
8 private String cname;
9 private Long pid;
10 private List<Category> children=new ArrayList<Category>();//这里为了防止后面空指针，初始化了children实例
11
12 public List<Category> getChildren() {
13 return children;
14 }
15
16 public void setChildren(List<Category> children) {
17 this.children = children;
18 }
19
20 public Long getCid() {
21 return cid;
22 }
23
24 public void setCid(Long cid) {
25 this.cid = cid;
26 }
27
28 public String getCname() {
29 return cname;
30 }
31
32 public void setCname(String cname) {
33 this.cname = cname;
34 }
35
36 public Long getPid() {
37 return pid;
38 }
39
40 public void setPid(Long pid) {
41 this.pid = pid;
42 }
43
44 @Override
45 public String toString() {
46 return "Category{cid:"+cid+
47 ",cname:"+cname+
48 ",pid:"+pid+
49 ",children:"+children+
50 "}";
51 }
52 }
3、写接口：
List<Category> findCategoriesByParentId(Long pid);自关联查询
List<Category> findAllCategories();一条sql查询所有，后期用Map算法分级
1 package cn.sohappy.acourses.course0921;
2
3 import cn.sohappy.acourses.bean.Category;
4
5 import java.util.List;
6
7 public interface ICategoryDAO {
8 List<Category> findCategoriesByParentId(Long pid);
9 List<Category> findAllCategories();
10 }
4、小配置：
1 <?xml version="1.0" encoding="UTF-8" ?>
2 <!DOCTYPE mapper
3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
5 <mapper namespace="cn.sohappy.acourses.course0921.ICategoryDAO">
6 <!--01.自关联查询-->
7 <resultMap id="selectCategoriesByPid" type="cn.sohappy.acourses.bean.Category">
8 <id property="cid" column="cid"/>
9 <result property="cname" column="cname"/>
10 <result property="pid" column="pid"/>
11 <collection property="children" ofType="cn.sohappy.acourses.bean.Category" select="findCategoriesByParentId" column="cid"/>
12 </resultMap>
13 <select id="findCategoriesByParentId" resultMap="selectCategoriesByPid">
14 select * from category where pid=#{0}
15 </select>
16 <!--02.单次查询-->
17 <resultMap id="MenuOneSQL" type="cn.sohappy.acourses.bean.Category" autoMapping="false">
18 <id property="cid" column="cid"/>
19 <result property="cname" column="cname"/>
20 <result property="pid" column="pid"/>
21 </resultMap>
22 <select id="findAllCategories" resultMap="MenuOneSQL">
23 select * from category
24 </select>
25 </mapper>
5.测试类：
1 package cn.test;
2
3 import cn.sohappy.acourses.bean.BillManyToOne;
4 import cn.sohappy.acourses.bean.Category;
5 import cn.sohappy.acourses.bean.UserOneToMany;
6 import cn.sohappy.acourses.course0921.ICategoryDAO;
7 import cn.sohappy.acourses.course0921.IUserDAO;
8 import cn.sohappy.acourses.course0921.InfiniteMenuUtil;
9 import cn.sohappy.bean.Smbms_user;
10 import cn.sohappy.util.MyBatisUtil;
11 import org.apache.ibatis.session.SqlSession;
12 import org.junit.Test;
13
14 import java.util.List;
15
16 public class test20170921 {
17 @Test
18 //自关联实现无穷分类
19 public void selfCorrelation(){
20 SqlSession session = MyBatisUtil.getSession();
21 ICategoryDAO mapper = session.getMapper(ICategoryDAO.class);
22 List<Category> categories = mapper.findCategoriesByParentId(0L);
23 for (Category item :categories) {
24 System.out.println(item);
25 }
26 session.close();
27 }
28 @Test
29 //Map集合实现无穷分类
30 public void InfiniteMenu(){
31 SqlSession session = MyBatisUtil.getSession();
32 ICategoryDAO mapper = session.getMapper(ICategoryDAO.class);
33 List<Category> categoriesClassified = new InfiniteMenuUtil().loadMenu(mapper.findAllCategories());
34 for (Category item :categoriesClassified) {
35 System.out.println(item);
36 }
37 session.close();
38 }
39 }
6、InfiniteMenu的Map算法
1 package cn.sohappy.acourses.course0921;
2
3 import java.lang.reflect.InvocationTargetException;
4 import java.lang.reflect.Method;
5 import java.util.*;
6
7 public class InfiniteMenuUtil {
8 @SuppressWarnings("unchecked")
9 public <T> List<T> loadMenu(List<T> menus) {
10 List<T> rootMenus = new ArrayList<T>();
11 if (menus != null && menus.size() != 0) {
12 List<Method> methodsList = Arrays.asList(menus.get(0).getClass().getDeclaredMethods());
13 //这里可以自己定制啦,我定制的是以pid,id,children结尾的get方法为分别getPid，getId，getChildren.所以menu类(Category)的属性名要符合定制规范
14 Method getId = null;
15 Method getPid = null;
16 Method getChildren = null;
17 //get getMethod
18 for (Method item : methodsList) {
19 if ("get".equals(item.getName().toLowerCase().substring(0,3))&&item.getName().length()>=6&&"pid".equals(item.getName().toLowerCase().substring(item.getName().length() - 3, item.getName().length()))){
20 getPid = item;
21 continue;
22 }
23 if ("get".equals(item.getName().toLowerCase().substring(0,3))&&item.getName().length()>=5&&"id".equals(item.getName().toLowerCase().substring(item.getName().length() - 2, item.getName().length()))){
24 getId = item;
25 continue;
26 }
27 if ("get".equals(item.getName().toLowerCase().substring(0,3))&&item.getName().length()>=11&&"children".equals(item.getName().toLowerCase().substring(item.getName().length() - 8, item.getName().length()))){
28 getChildren = item;
29 }
30 }
31 if (getId!=null&&getPid!=null&&getChildren!=null){
32 //get menuMap
33 Map<Long, T> menuMap = new HashMap<Long, T>();
34 for (T menu : menus) {
35 Long id = null;
36 try {
37 id = (Long)getId.invoke(menu);
38 } catch (IllegalAccessException e) {
39 e.printStackTrace();
40 } catch (InvocationTargetException e) {
41 e.printStackTrace();
42 }
43 menuMap.put(id,menu);
44 }
45 //add children
46 for (T menu:menus) {
47 Long pid = null;
48 try {
49 pid = (Long)getPid.invoke(menu);
50 } catch (IllegalAccessException e) {
51 e.printStackTrace();
52 } catch (InvocationTargetException e) {
53 e.printStackTrace();
54 }
55 if (pid==null||pid==0){
56 rootMenus.add(menu);
57 }else {
58 T t = menuMap.get(pid);
59 List<T> ts;
60 try {
61 ts = (List<T>) getChildren.invoke(t);
62 ts.add(menu);
63 } catch (IllegalAccessException e) {
64 e.printStackTrace();
65 } catch (InvocationTargetException e) {
66 e.printStackTrace();
67 }
68 }
69 }
70 }
71 }
72 return rootMenus;
73 }
74 }
时间： 2024-10-11 11:55:08