Example code for building a tree menu (including multi-level menu) in Java

This article mainly introduces the example code for building a tree menu in Java (supporting multi-level menus). It is very good and has reference value. Friends in need can refer to the

renderings: support multi-level menus menu.

Menu entity class:

public class Menu {
  // 菜单id
  private String id;
  // 菜单名称
  private String name;
  // 父菜单id
  private String parentId;
  // 菜单url
  private String url;
  // 菜单图标
  private String icon;
  // 菜单顺序
  private int order;
  // 子菜单
  private List<Menu> children;
  // ... 省去getter和setter方法以及toString方法
}

Menus generally need to be sorted, we sort according to the order field of Menu:

　/*
   * 排序,根据order排序
   */
  public Comparator<Menu> order(){
    Comparator<Menu> comparator = new Comparator<Menu>() {
      @Override
      public int compare(Menu o1, Menu o2) {
        if(o1.getOrder() != o2.getOrder()){
          return o1.getOrder() - o2.getOrder();
        }
        return 0;
      }
    };
    return comparator;
  }

Generating tree Method:

public Map<String,Object> findTree(){
  Map<String,Object> data = new HashMap<String,Object>();
    try {//查询所有菜单
      List<Menu> allMenu = menuDao.findTree();
      //根节点
      List<Menu> rootMenu = new ArrayList<Menu>();
      for (Menu nav : allMenu) {
        if(nav.getParentId().equals("0")){//父节点是0的，为根节点。
          rootMenu.add(nav);
        }
      }
      /* 根据Menu类的order排序 */
      Collections.sort(rootMenu, order());
      //为根菜单设置子菜单，getClild是递归调用的
      for (Menu nav : rootMenu) {
        /* 获取根节点下的所有子节点 使用getChild方法*/
        List<Menu> childList = getChild(nav.getId(), allMenu);
        nav.setChildren(childList);//给根节点设置子节点
      }
      /**
       * 输出构建好的菜单数据。
       * 
       */
      data.put("success", "true");
      data.put("list", rootMenu);
      return data;
    } catch (Exception e) {
      data.put("success", "false");
      data.put("list", new ArrayList());
      return data;
    }
  }

Get submenu:

/**
   * 获取子节点
   * @param id 父节点id
   * @param allMenu 所有菜单列表
   * @return 每个根节点下，所有子菜单列表
   */
  public List<Menu> getChild(String id,List<Menu> allMenu){
    //子菜单
    List<Menu> childList = new ArrayList<Menu>();
    for (Menu nav : allMenu) {
      // 遍历所有节点，将所有菜单的父id与传过来的根节点的id比较
      //相等说明：为该根节点的子节点。
      if(nav.ParentId().equals(id)){
        childList.add(nav);
      }
    }
    //递归
    for (Menu nav : childList) {
      nav.setChildren(getChild(nav.getId(), allMenu));
    }
    Collections.sort(childList,order());//排序
    //如果节点下没有子节点，返回一个空List（递归退出）
    if(childList.size() == 0){
      return new ArrayList<Menu>();
    }
    return childList;
  }

The final JSON string returned is as follows:

{
 "success": "true",
 "list": [
   {
    "id": "1",
    "name": "Java",
    "parentid": "0",
    "url": "http://www.php.cn",
    "order": 1,
    "children": [
     {
       "id": "2",
       "name": "并发编程",
       "parentid": "1",
       "url": "http://www.php.cn",
       "order": 1,
       "children": []
     },
     {
       "id": "3",
       "name": "多线程",
       "parentid": "1",
       "url": "http://www.php.cn",
       "order": 2,
       "children": [
         "id": "4",
         "name": "Thread",
         "parentid": "3",
         "url": "http://www.php.cn",
         "order": 1,
　　　　　　　　　　"children":[]
       ]
     }
    ]
   },
   {
    "id": "5",
    "name": "Python",
    "parentid": "0",
    "url": "http://www.php.cn",
    "order": 2,
    "children": []
   }
  ]
}

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