场景说明：

在项目实际过程中，经常遇见 二维表 （数据库表）为树形结构存储数据，但是递归查询需要好多次，特别是数据量大时，变得非常不合适~

以下是项目中，将列表转换组装为树形结构的代码共享~

平铺的数据：

参考代码案例：

 import com.sxmfyy.health.model.system.menu.HealthSysMenu;
import com.sxmfyy.health.model.system.menu.dto.HealthSysMenuDTO;
import org.springframework.beans.BeanUtils;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class TileTreeConverter {

    /**
     * 算法====>将平铺结构转换为树形结构
     * 实现方案====>采用递归方式
     *
     * @param sysMenuList
     * @return
     */
    public static List<HealthSysMenuDTO> convertTree(List<HealthSysMenu> sysMenuList) {
        if (sysMenuList == null || sysMenuList.size() <= 0) {
            return new ArrayList<HealthSysMenuDTO>();
        }
        int topSign = -1;
        List<HealthSysMenuDTO> healthSysMenuDTOList = findChildren(sysMenuList, topSign);
        buildTree(sysMenuList, healthSysMenuDTOList);
        return healthSysMenuDTOList;
    }

    /**
     * @param sysMenuList
     * @param parentId
     * @return
     */
    private static List<HealthSysMenuDTO> findChildren(List<HealthSysMenu> sysMenuList, int parentId) {
        // 根据父节点找到子节点，以集合的形式返回
        List<HealthSysMenuDTO> healthSysMenuDTOList = new ArrayList<HealthSysMenuDTO>();
        for (HealthSysMenu healthSysMenu : sysMenuList) {
            if (parentId == healthSysMenu.getParentId()) {
                HealthSysMenuDTO healthSysMenuDTO = new HealthSysMenuDTO();
                healthSysMenuDTO.setId(healthSysMenu.getMenuId());
                healthSysMenuDTO.setParentId(healthSysMenu.getParentId());
                BeanUtils.copyProperties(healthSysMenu, healthSysMenuDTO);
                healthSysMenuDTOList.add(healthSysMenuDTO);
            }
        }
        sorted(healthSysMenuDTOList);
        return healthSysMenuDTOList;
    }

    /**
     * @param sysMenuList
     * @param sysMenuDTOList
     * @return
     */
    private static void buildTree(List<HealthSysMenu> sysMenuList, List<HealthSysMenuDTO> sysMenuDTOList) {
        // 如果存在子节点，再次递归子节点
        if (sysMenuDTOList != null && sysMenuDTOList.size() > 0) {
            for (HealthSysMenuDTO healthSysMenuDTO : sysMenuDTOList) {
                List<HealthSysMenuDTO> subSysMenuDTOList = findChildren(sysMenuList, healthSysMenuDTO.getParentId());
                if (subSysMenuDTOList != null && subSysMenuDTOList.size() > 0) {
                    healthSysMenuDTO.setChildren(subSysMenuDTOList);
                }
            }
        }
    }

    /**
     * 排序
     * @param healthSysMenuDTOList
     */
    private static void sorted(List<HealthSysMenuDTO> healthSysMenuDTOList){
        Collections.sort(healthSysMenuDTOList,new Comparator<HealthSysMenuDTO>() {

            @Override
            public int compare(HealthSysMenuDTO t1, HealthSysMenuDTO t2) {
                if(t1.getSort() > t2.getSort()){
                    return 1;
                }else if(t1.getSort() < t2.getSort()){
                    return -1;
                }
                return 0;
            }
        });
    }


    /**
     * main方法==>测试验证
     *
     * @param args
     */
    public static void main(String[] args) {
        List<HealthSysMenu> sysMenuList = new ArrayList<HealthSysMenu>();
        // 构建顶层节点，其父节点为"-1"
        HealthSysMenu healthSysMenu1001 = new HealthSysMenu();
        healthSysMenu1001.setMenuId(1001L);
        healthSysMenu1001.setParentId(-1);
        healthSysMenu1001.setName("1001");
        healthSysMenu1001.setSort(1);
        sysMenuList.add(healthSysMenu1001);
        HealthSysMenu healthSysMenu1002 = new HealthSysMenu();
        healthSysMenu1002.setMenuId(1002L);
        healthSysMenu1002.setParentId(-1);
        healthSysMenu1002.setName("1002");
        healthSysMenu1002.setSort(3);
        sysMenuList.add(healthSysMenu1002);
        HealthSysMenu healthSysMenu1003 = new HealthSysMenu();
        healthSysMenu1003.setMenuId(1003L);
        healthSysMenu1003.setParentId(-1);
        healthSysMenu1003.setName("1003");
        healthSysMenu1003.setSort(2);
        sysMenuList.add(healthSysMenu1003);
        // 构建节点的子节点
        HealthSysMenu healthSysMenu100101 = new HealthSysMenu();
        healthSysMenu100101.setMenuId(100101L);
        healthSysMenu100101.setParentId(1001);
        healthSysMenu100101.setName("100101");
        healthSysMenu100101.setSort(1);
        sysMenuList.add(healthSysMenu100101);
        HealthSysMenu healthSysMenu100102 = new HealthSysMenu();
        healthSysMenu100102.setMenuId(100102L);
        healthSysMenu100102.setParentId(1001);
        healthSysMenu100102.setName("100102");
        healthSysMenu100102.setSort(3);
        sysMenuList.add(healthSysMenu100102);
        HealthSysMenu healthSysMenu100103 = new HealthSysMenu();
        healthSysMenu100103.setMenuId(100103L);
        healthSysMenu100103.setParentId(1001);
        healthSysMenu100103.setName("100102");
        healthSysMenu100103.setSort(2);
        sysMenuList.add(healthSysMenu100103);
        // 转换成树形结构对象
        List<HealthSysMenuDTO> convertTree = convertTree(sysMenuList);
        System.out.println(convertTree);
    }


}
  

代码案例的执行效果：