CREATE TABLE `sys_area` 
(  `id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主鍵ID',
`parent_id` bigint(20) DEFAULT NULL COMMENT '父級(jí)ID', 
`name` varchar(50) NOT NULL COMMENT '地區(qū)名稱',
`level` int(11) NOT NULL COMMENT '層級(jí)(1:省份 2:城市 3:區(qū)縣)',
`sort` int(11) DEFAULT 0 COMMENT '排序號(hào)',  
`status` tinyint(4) DEFAULT 1 COMMENT '狀態(tài)(0:禁用 1:啟用)',  
`create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '創(chuàng)建時(shí)間', 
`update_time` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新時(shí)間', 
PRIMARY KEY (`id`),  
KEY `idx_parent_id` (`parent_id`)) 
ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='地區(qū)表';

@Data
public class Area implements Serializable {
      private static final long serialVersionUID = 1L;
          // 主鍵ID    
          private Long id;
          // 父級(jí)ID
          private Long parentId;
          // 地區(qū)名稱
          private String name;
          // 層級(jí)   
          private Integer level; 
          // 排序號(hào)   
          private Integer sort;   
          // 狀態(tài)   
          private Integer status;
          // 創(chuàng)建時(shí)間   
          private Date createTime;
          // 更新時(shí)間    
          private Date updateTime;  
          // 子節(jié)點(diǎn)列表   
          private List<Area> children;
      }

@Mapper
public interface AreaMapper {
    /**     
    * 查詢所有地區(qū)數(shù)據(jù)    
    * @return 地區(qū)列表     */  
    List<Area> selectAllAreas(); 
    /**     
    * 根據(jù)父ID查詢子地區(qū)     
    * @param parentId 父級(jí)ID     
    * @return 子地區(qū)列表     */   
    List<Area> selectAreasByParentId(Long parentId);        
    /**    
    * 查詢指定層級(jí)的地區(qū)     
    * @param level 層級(jí)    
    * @return 地區(qū)列表     */  
    List<Area> selectAreasByLevel(Integer level);
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.mapper.AreaMapper">
    <!-- 基礎(chǔ)列 -->  
    <sql id="Base_Column_List"> 
        id, parent_id, name, level, sort, status, create_time, update_time   
    </sql>       
    <!-- 查詢所有地區(qū) --> 
    <select id="selectAllAreas" resultType="com.example.entity.Area"> 
        SELECT   <include refid="Base_Column_List"/>    FROM sys_area 
        WHERE status = 1      
        ORDER BY sort ASC, id ASC   
    </select>       
    <!-- 根據(jù)父ID查詢子地區(qū) -->  
    <select id="selectAreasByParentId" resultType="com.example.entity.Area"> 
        SELECT     <include refid="Base_Column_List"/>     FROM sys_area        
        WHERE status = 1        
        AND parent_id = #{parentId}       
        ORDER BY sort ASC, id ASC   
    </select>      
    <!-- 查詢指定層級(jí)的地區(qū) -->   
    <select id="selectAreasByLevel" resultType="com.example.entity.Area">  
        SELECT     <include refid="Base_Column_List"/>    FROM sys_area        
        WHERE status = 1     
        AND level = #{level}    
        ORDER BY sort ASC, id ASC  
    </select>
</mapper>

@Service
@Slf4j
public class AreaServiceImpl implements AreaService {
    @Autowired
    private AreaMapper areaMapper; 
    @Override
    public List<Area> buildAreaTree() { 
        // 查詢所有地區(qū)數(shù)據(jù) 
        List<Area> allAreas = areaMapper.selectAllAreas(); 
        // 構(gòu)建樹(shù)形結(jié)構(gòu)
        return buildTree(allAreas);
    } 
    /**
    * 構(gòu)建樹(shù)形結(jié)構(gòu) 
    * @param areas 地區(qū)列表 
    * @return 樹(shù)形結(jié)構(gòu)的地區(qū)列表 
    */ 
    private List<Area> buildTree(List<Area> areas) { 
        List<Area> trees = new ArrayList<>(); 
        // 獲取所有根節(jié)點(diǎn)(省份)
        areas.stream().filter(area -> area.getLevel() == 1) .forEach(province -> { 
            // 設(shè)置省份的子節(jié)點(diǎn)(城市) 
            List<Area> cities = getChildren(areas, province.getId()); 
            province.setChildren(cities); 
            // 設(shè)置城市的子節(jié)點(diǎn)(區(qū)縣)
            cities.forEach(city -> { List<Area> districts = getChildren(areas, city.getId());   
                city.setChildren(districts);  
            });
            trees.add(province);
        });
        return trees; 
    } 
    /**
    * 獲取子節(jié)點(diǎn) 
    * @param areas 所有地區(qū)列表 
    * @param parentId 父級(jí)ID 
    * @return 子節(jié)點(diǎn)列表
    */ 
    private List<Area> getChildren(List<Area> areas, Long parentId) { 
        return areas.stream().filter(area -> Objects.equals(area.getParentId(), parentId)) 
        .collect(Collectors.toList()); 
    }
}

@RestController@RequestMapping("/api/areas")
public class AreaController {   
    @Autowired   
    private AreaService areaService;    
    /**    
    * 獲取地區(qū)樹(shù)形數(shù)據(jù)     */ 
    @GetMapping("/tree")   
    public ResponseResult<List<Area>> getAreaTree() { 
        try {       
            List<Area> trees = areaService.buildAreaTree();   
            return ResponseResult.success(trees);    
        } catch (Exception e) {   
            log.error("獲取地區(qū)樹(shù)形數(shù)據(jù)失敗", e);    
            return ResponseResult.error("獲取地區(qū)樹(shù)形數(shù)據(jù)失敗");     
        }  
   }
}

@Service
public class AreaServiceImpl implements AreaService {
    @Autowired   
    private RedisTemplate<String, List<Area>> redisTemplate; 
    private static final String AREA_TREE_KEY = "AREA:TREE";  
    private static final long CACHE_TIMEOUT = 24; 
    // 小時(shí)   
    @Override   
    public List<Area> buildAreaTree() {
        // 先從緩存獲取  
        List<Area> cacheTree = redisTemplate.opsForValue().get(AREA_TREE_KEY);   
        if (cacheTree != null) {   
            return cacheTree;  
        }               
        // 緩存未命中，查詢數(shù)據(jù)庫(kù)并構(gòu)建樹(shù)    
        List<Area> trees = buildTreeFromDb();       
        // 放入緩存    
        redisTemplate.opsForValue().set(AREA_TREE_KEY, trees, CACHE_TIMEOUT, TimeUnit.HOURS);                return trees;
    }
}