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

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 children; // ... 省去getter和setter方法以及toString方法 }

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

public Map findTree(){ Map data = new HashMap(); try {//查询所有菜单 List allMenu = menuDao.findTree(); //根节点 List rootMenu = new ArrayList(); 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 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; } }

/** * 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 getChild(String id,List allMenu){ //子菜单 List childList = new ArrayList(); 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(); } return childList; }

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