@Override

    public List<YjztCity> getYjzt(){

        List<YjztCity> yjztCities = yjztCityMapper.selectByExample(null);  //先获取你想要在哪些菜单范围内搜索

        List<YjztCity> rootMenus = new ArrayList<>();

        for (YjztCity menu : yjztCities) {

            //从最上级菜单开始展示

            if(menu.getType().equals("2")){

                rootMenus.add(menu);

            }

        }

        for (YjztCity rootMenu : rootMenus) {

            //把最上级菜单的子菜单获取到，子菜单的子菜单也会获取到(目前是三层，由于是递归调用，100层也没问题)

            List<YjztCity> child = getChild(rootMenu.getZfwqydm(), yjztCities);

            rootMenu.setChildren(child);

        }

        return rootMenus;

    }

    private List<YjztCity> getChild(String id,List<YjztCity> menus){

        List<YjztCity> childList = new ArrayList<>();

        for (YjztCity menu : menus) {

            if(menu.getZfwsjqydm().equals(id)){

                //当菜单范围内的父id等于传入的id,获取该id的所有子列表

                childList.add(menu);

            }

        }

        for (YjztCity menu : childList) {

            //当上面循环语句查询不到子菜单，长度为0，自然也就不会递归调用了

            //将该id的子菜单便利，通过递归调用，给每一个子菜单赋值子菜单

            List<YjztCity> child = getChild(menu.getZfwqydm(), menus);

            menu.setChildren(child);

        }

        if(childList.size()==0){

            //子菜单的长度为0,返回null,null不会被jackson解析

            return null;

        }

        return childList;

    }