MyBatis无限级分类实现的两种方法--自关联与map集合

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:

package cn.sohappy.acourses.bean;

import java.util.ArrayList;
import java.util.List;

public class Category {
    private Long cid;
    private String cname;
    private Long pid;
    private List<Category> children;

   //省略getter and setter
}

然后初始化children并重写toString方法方便测试，完整代码如下：

package cn.sohappy.acourses.bean;

import java.util.ArrayList;
import java.util.List;

public class Category {
    private Long cid;
    private String cname;
    private Long pid;
    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

    public List<Category> getChildren() {
        return children;
    }

    public void setChildren(List<Category> children) {
        this.children = children;
    }

    public Long getCid() {
        return cid;
    }

    public void setCid(Long cid) {
        this.cid = cid;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }

    public Long getPid() {
        return pid;
    }

    public void setPid(Long pid) {
        this.pid = pid;
    }

    @Override
    public String toString() {
        return "Category{cid:"+cid+
                ",cname:"+cname+
                ",pid:"+pid+
                ",children:"+children+
                "}";
    }
}

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

package cn.sohappy.acourses.course0921;

import cn.sohappy.acourses.bean.Category;

import java.util.List;

public interface ICategoryDAO {
    List<Category> findCategoriesByParentId(Long pid);
    List<Category> findAllCategories();
}

4、小配置：

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="cn.sohappy.acourses.course0921.ICategoryDAO">
    <!--01.自关联查询-->
    <resultMap id="selectCategoriesByPid" type="cn.sohappy.acourses.bean.Category">
        <id property="cid" column="cid"/>
        <result property="cname" column="cname"/>
        <result property="pid" column="pid"/>
        <collection property="children" ofType="cn.sohappy.acourses.bean.Category" select="findCategoriesByParentId" column="cid"/>
    </resultMap>
    <select id="findCategoriesByParentId" resultMap="selectCategoriesByPid">
        select * from category where pid=#{0}
    </select>
    <!--02.单次查询-->
    <resultMap id="MenuOneSQL" type="cn.sohappy.acourses.bean.Category" autoMapping="false">
        <id property="cid" column="cid"/>
        <result property="cname" column="cname"/>
        <result property="pid" column="pid"/>
    </resultMap>
    <select id="findAllCategories" resultMap="MenuOneSQL">
        select * from category
    </select>
</mapper>

5.测试类：

package cn.test;

import cn.sohappy.acourses.bean.BillManyToOne;
import cn.sohappy.acourses.bean.Category;
import cn.sohappy.acourses.bean.UserOneToMany;
import cn.sohappy.acourses.course0921.ICategoryDAO;
import cn.sohappy.acourses.course0921.IUserDAO;
import cn.sohappy.acourses.course0921.InfiniteMenuUtil;
import cn.sohappy.bean.Smbms_user;
import cn.sohappy.util.MyBatisUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class test20170921 {
    @Test
    //自关联实现无穷分类
    public void selfCorrelation(){
        SqlSession session = MyBatisUtil.getSession();
        ICategoryDAO mapper = session.getMapper(ICategoryDAO.class);
        List<Category> categories = mapper.findCategoriesByParentId(0L);
        for (Category item :categories) {
            System.out.println(item);
        }
        session.close();
    }
    @Test
    //Map集合实现无穷分类
    public void InfiniteMenu(){
        SqlSession session = MyBatisUtil.getSession();
        ICategoryDAO mapper = session.getMapper(ICategoryDAO.class);
        List<Category> categoriesClassified = new InfiniteMenuUtil().loadMenu(mapper.findAllCategories());
        for (Category item :categoriesClassified) {
            System.out.println(item);
        }
        session.close();
    }
}

6、InfiniteMenu的Map算法

package cn.sohappy.acourses.course0921;

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.*;

public class InfiniteMenuUtil {
    @SuppressWarnings("unchecked")
    public <T> List<T> loadMenu(List<T> menus) {
        List<T> rootMenus = new ArrayList<T>();
        if (menus != null && menus.size() != 0) {
            List<Method> methodsList = Arrays.asList(menus.get(0).getClass().getDeclaredMethods());
            //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
            Method getId = null;
            Method getPid = null;
            Method getChildren = null;
            //get getMethod
            for (Method item : methodsList) {
                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()))){
                    getPid = item;
                    continue;
                }
                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()))){
                    getId = item;
                    continue;
                }
                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()))){
                    getChildren = item;
                }
            }
            if (getId!=null&&getPid!=null&&getChildren!=null){
                //get menuMap
                Map<Long, T> menuMap = new HashMap<Long, T>();
                for (T menu : menus) {
                    Long id = null;
                    try {
                        id = (Long)getId.invoke(menu);
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    } catch (InvocationTargetException e) {
                        e.printStackTrace();
                    }
                    menuMap.put(id,menu);
                }
                //add children
                for (T menu:menus) {
                    Long pid = null;
                    try {
                        pid = (Long)getPid.invoke(menu);
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    } catch (InvocationTargetException e) {
                        e.printStackTrace();
                    }
                    if (pid==null||pid==0){
                        rootMenus.add(menu);
                    }else {
                        T t = menuMap.get(pid);
                        List<T> ts;
                        try {
                            ts = (List<T>) getChildren.invoke(t);
                            ts.add(menu);
                        } catch (IllegalAccessException e) {
                            e.printStackTrace();
                        } catch (InvocationTargetException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
        return rootMenus;
    }
}