Java实现一个简易版的多级菜单功能

DROP TABLE IF EXISTS `t_category`;
CREATE TABLE `t_category` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '标识目录的唯一id',
  `parent_id` int(11) DEFAULT NULL COMMENT '存储父级目录的id，0代表一级目录',
  `name` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '目录的名称',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

public class Category {
    private int id;
    private int parentId;
    private String name;
}

public class CategoryTwo extends Category{
    private List<CategoryTwo> categorieTwos;
 
    public CategoryTwo(){}
 
    //这个有参构造方法方便我们为属性赋值即把categoy的成员变量的值赋值到自身中
    public CategoryTwo(Category category){
        super(category.getId(),category.getParentId(),category.getName());
    }
}

//多级目录
    public void findCategoryAll(){
 
        //查询出所有的目录数据
        List<Category> categorys = categoryMapper.findCategoryAll(null);//这个大家自己完成
 
 
        //存放所有一级目录
        List<CategoryTwo> categoryTows = new ArrayList();
 
        //找出一级目录，即 parentId = 0 的目录
        for(Category category :categorys){
            if(category.getParentId() == 0){
                CategoryTwo categoryTwo = new CategoryTwo(category);
                categoryTows.add(categoryTwo);//存入一级目录集合中
            }
        }
 
        //利用递归，找出所有一级目录的List<CategoryTwo>,这里我把具体实现包装到 findSubCategory（）方法中了
        categoryTows = findSubCategory(categorys,categoryTows);
 
        //最后就完成了，把数据按需求返回给前端就可以了。
        System.out.println(categoryTows);
    }
 
    //找出List<CategoryTwo>中所有目录的子级目录
    public List<CategoryTwo> findSubCategory(List<Category> categorys,List<CategoryTwo> categoryTwos){
 
        for (CategoryTwo categoryTwo:categoryTwos) {
            //找出自身的子级目录，存放到List<CategoryTwo>中去
            List<CategoryTwo> categoryTwos2 = new ArrayList<CategoryTwo>();
 
            for (Category category:categorys){
                //如果自身的id = 与某个目录的parentId 相等，则这个目录是自身的子级目录
                if(categoryTwo.getId() == category.getParentId()){
                    categoryTwos2.add(new CategoryTwo(category));
                }
            }
 
            //所有子级目录找到后，再回调findSubCategory()方法 让子级目录找到自己的子级
            List<CategoryTwo> categoryTwos3 = findSubCategory(categorys,categoryTwos2);
 
            //categoryTwos3真正的List<categoryTwo>，把他添加到自身
            categoryTwo.setCategorieTwos(categoryTwos3);
        }
 
        return categoryTwos;//返回注入好的对象
    }

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
 
 
public class MenuTest {
 
    /**
     * @param args
     */
    public static void main(String[] args) {
        MenuTest menuTest = new MenuTest();
        List menuList = initMenu();//初始化菜单
        Map menuMap = menuTest.rebuildMenus(menuList);//重构菜单
        menuTest.showMenu(menuMap);//打印菜单
 
    }
     
    /**
     * 重构菜单，构造成需要的结构
     * @param menuList
     * @return
     */
    private Map rebuildMenus(List menuList) {
        List rootMenuList=new ArrayList();//这个List用来存放根菜单
        for (int j = 0; j < menuList.size(); j++) {
            Map menu = (Map) menuList.get(j);
            String parentId = menu.get("parentId").toString();
            if (null==parentId || "".equals(parentId)) {
                rootMenuList.add(menu);
            }
        }
        menuList.removeAll(rootMenuList);//将根菜单从menuList中除去
        HashMap menuMap = new HashMap();
        for (int j = 0; j < rootMenuList.size(); j++) {//遍历根菜单，每一个跟菜单都遍历到最后一个子菜单（叶子节点）
            Map menu = (Map) rootMenuList.get(j);
            menu = this.pase(menu, menuList);
            menuMap.put(menu.get("id"), menu);
        }
        return menuMap;
    }
 
    /**
     * 递归构造菜单Map
     * @param menu
     * @param menuList
     * @return
     */
    private Map pase(Map menu, List menuList) {
        for (int j = 0; j < menuList.size(); j++) {
            Map menu2 = (Map) menuList.get(j);
            if (menu2.get("parentId").toString().equals(menu.get("id").toString())) {
                if(menu.get("children") == null){
                    menu.put("children", new ArrayList());
                }
                ((List)menu.get("children")).add(menu2);
                pase(menu2, menuList);
            }
        }
        return menu;
    }
    /**
     * 打印菜单
     * @param menuMap
     */
    private void showMenu(Map menuMap){
        Iterator it = menuMap.keySet().iterator();
        while(it.hasNext()){
            Map menu = (Map) menuMap.get(it.next());
            System.out.println(menu.get("id")+"--"+menu.get("name"));
            this.buildChildMenu(menu);
        }
    }
    /**
     * 构造子菜单
     * @param menu
     */
    private void buildChildMenu(Map menu){
        List childList = (List) menu.get("children");
        if(null!=childList){
            for(int i=0;i<childList.size();i++){
                Map childMap = (Map) childList.get(i);
                System.out.println(childMap.get("id")+"--"+childMap.get("name"));
                this.buildChildMenu(childMap);
            }
        }
    }
    /**
     * 初始化菜单，实际项目中这部分数据是从数据库中获取
     * @return
     */
    public static List initMenu(){
        List menuList = new ArrayList();
         
        Map menuMap = new HashMap();
        menuMap.put("id", "0000");
        menuMap.put("name", "根菜单");
        menuMap.put("parentId","");//根菜单的父菜单为空
         
        Map menuMap1 = new HashMap();
        menuMap1.put("id", "1000");
        menuMap1.put("name", "一级菜单A");
        menuMap1.put("parentId","0000");
         
        Map menuMap2 = new HashMap();
        menuMap2.put("id", "2000");
        menuMap2.put("name", "一级菜单B");
        menuMap2.put("parentId","0000");
         
        Map menuMap3 = new HashMap();
        menuMap3.put("id", "1100");
        menuMap3.put("name", "二级菜单A");
        menuMap3.put("parentId","1000");
         
        Map menuMap4 = new HashMap();
        menuMap4.put("id", "1110");
        menuMap4.put("name", "三级菜单A");
        menuMap4.put("parentId","1100");
         
        menuList.add(menuMap);
        menuList.add(menuMap1);
        menuList.add(menuMap2);
        menuList.add(menuMap3);
        menuList.add(menuMap4);
         
        return menuList;
    }
     
     
 
}