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前言
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一、需求场景
实际开发中，后端需要返回树形结构数据，比如：部门树
二、数据库表
表结构展示：
三.实现方式
1.方式1:
方式1是通过mybatis的递归查询实现
代码如下（示例）：
实体类对象：
@TableName(value ="t_department")@Datapublic class Department implements Serializable { @TableId(value = "id", type = IdType.AUTO) private Integer id; @TableField(value = "name") private String name; @TableField(value = "parentId") private Integer parentId; @TableField(value = "depPath") private String depPath; @TableField(value = "enabled") private Integer enabled; @TableField(value = "isParent") private Integer isParent; @TableField(exist = false) private List<Department> children; @TableField(exist = false) private static final long serialVersionUID = 1L;}mapper层代码：
public interface DepartmentMapper extends BaseMapper<Department> { List<Department> getAllById(Integer id);}service层
@Override public List<Department> getAll() { return departmentMapper.getAllById(-1); }xml展示：
<resultMap id="BaseResultMap" type="org.example.domain.Department"> <id property="id" column="id" jdbcType="INTEGER"/> <result property="name" column="name" jdbcType="VARCHAR"/> <result property="parentId" column="parentId" jdbcType="INTEGER"/> <result property="depPath" column="depPath" jdbcType="VARCHAR"/> <result property="enabled" column="enabled" jdbcType="TINYINT"/> <result property="isParent" column="isParent" jdbcType="TINYINT"/> </resultMap> <resultMap id="DepartmentMap" type="org.example.domain.Department" extends="BaseResultMap"> <collection property="children" ofType="org.example.domain.Department" column="id" select="org.example.mapper.DepartmentMapper.getAllById"> </collection> </resultMap> <sql id="Base_Column_List"> id,name,parentId, depPath,enabled,isParent </sql> <select id="getAllById" resultMap="DepartmentMap"> select <include refid="Base_Column_List" /> from t_department where parentId = #{id} </select>主要是通过collection标签实现递归查询，首先查询根节点，然后返回的id依次去查询子节点
测试：
@Test public void testGetDepartments1(){ List<Department> list = departmentService.getAll(); System.out.println(JSON.toJSONString(list)); }输出结果：
==> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==> Parameters: -1(Integer)<== Columns: id, name, parentId, depPath, enabled, isParent<== Row: 1, 股东会, -1, .1, 1, 1====> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?====> Parameters: 1(Integer)<==== Columns: id, name, parentId, depPath, enabled, isParent<==== Row: 2, 董事会, 1, .1.2, 1, 1======> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?======> Parameters: 2(Integer)<====== Columns: id, name, parentId, depPath, enabled, isParent<====== Row: 3, 总办, 2, .1.2.3, 1, 1========> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?========> Parameters: 3(Integer)<======== Columns: id, name, parentId, depPath, enabled, isParent<======== Row: 4, 财务部, 3, .1.2.3.4, 1, 0==========> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==========> Parameters: 4(Integer)<========== Total: 0<======== Row: 5, 市场部, 3, .1.2.3.5, 1, 1==========> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==========> Parameters: 5(Integer)<========== Columns: id, name, parentId, depPath, enabled, isParent<========== Row: 6, 华东市场部, 5, 1.2.3.5.6, 1, 1============> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?============> Parameters: 6(Integer)<============ Columns: id, name, parentId, depPath, enabled, isParent<============ Row: 8, 上海市场部, 6, 1.2.3.5.6.8, 1, 0==============> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==============> Parameters: 8(Integer)<============== Total: 0<============ Total: 1<========== Row: 7, 华南市场部, 5, 1.2.3.5.7, 1, 0============> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?============> Parameters: 7(Integer)<============ Total: 0<========== Row: 9, 西北市场部, 5, .1.2.3.5.9, 1, 1============> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?============> Parameters: 9(Integer)<============ Columns: id, name, parentId, depPath, enabled, isParent<============ Row: 10, 贵阳市场, 9, .1.2.3.5.9.10, 1, 1==============> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==============> Parameters: 10(Integer)<============== Columns: id, name, parentId, depPath, enabled, isParent<============== Row: 11, 乌当区市场, 10, .1.2.3.5.9.10.11, 1, 0================> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?================> Parameters: 11(Integer)<================ Total: 0<============== Total: 1<============ Total: 1<========== Total: 3<======== Row: 12, 技术部, 3, .1.2.3.12, 1, 0==========> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==========> Parameters: 12(Integer)<========== Total: 0<======== Row: 13, 运维部, 3, .1.2.3.13, 1, 0==========> Preparing: select id,name,parentId, depPath,enabled,isParent from t_department where parentId = ?==========> Parameters: 13(Integer)<========== Total: 0<======== Total: 4<====== Total: 1<==== Total: 1<== Total: 1Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@437281c5][{"children":[{"children":[{"children":[{"children":[],"depPath":".1.2.3.4","enabled":1,"id":4,"isParent":0,"name":"财务部","parentId":3},{"children":[{"children":[{"children":[],"depPath":"1.2.3.5.6.8","enabled":1,"id":8,"isParent":0,"name":"上海市场部","parentId":6}],"depPath":"1.2.3.5.6","enabled":1,"id":6,"isParent":1,"name":"华东市场部","parentId":5},{"children":[],"depPath":"1.2.3.5.7","enabled":1,"id":7,"isParent":0,"name":"华南市场部","parentId":5},{"children":[{"children":[{"children":[],"depPath":".1.2.3.5.9.10.11","enabled":1,"id":11,"isParent":0,"name":"乌当区市场","parentId":10}],"depPath":".1.2.3.5.9.10","enabled":1,"id":10,"isParent":1,"name":"贵阳市场","parentId":9}],"depPath":".1.2.3.5.9","enabled":1,"id":9,"isParent":1,"name":"西北市场部","parentId":5}],"depPath":".1.2.3.5","enabled":1,"id":5,"isParent":1,"name":"市场部","parentId":3},{"children":[],"depPath":".1.2.3.12","enabled":1,"id":12,"isParent":0,"name":"技术部","parentId":3},{"children":[],"depPath":".1.2.3.13","enabled":1,"id":13,"isParent":0,"name":"运维部","parentId":3}],"depPath":".1.2.3","enabled":1,"id":3,"isParent":1,"name":"总办","parentId":2}],"depPath":".1.2","enabled":1,"id":2,"isParent":1,"name":"董事会","parentId":1}],"depPath":".1","enabled":1,"id":1,"isParent":1,"name":"股东会","parentId":-1}]部门树结构：
[ { "children":[ { "children":[ { "children":[{ "children":[ ], "depPath":".1.2.3.4", "enabled":1, "id":4, "isParent":0, "name":"财务部", "parentId":3},{ "children":[ { "children":[ { "children":[ ], "depPath":"1.2.3.5.6.8", "enabled":1, "id":8, "isParent":0, "name":"上海市场部", "parentId":6 } ], "depPath":"1.2.3.5.6", "enabled":1, "id":6, "isParent":1, "name":"华东市场部", "parentId":5 }, { "children":[ ], "depPath":"1.2.3.5.7", "enabled":1, "id":7, "isParent":0, "name":"华南市场部", "parentId":5 }, { "children":[ { "children":[ {"children":[],"depPath":".1.2.3.5.9.10.11","enabled":1,"id":11,"isParent":0,"name":"乌当区市场","parentId":10 } ], "depPath":".1.2.3.5.9.10", "enabled":1, "id":10, "isParent":1, "name":"贵阳市场", "parentId":9 } ], "depPath":".1.2.3.5.9", "enabled":1, "id":9, "isParent":1, "name":"西北市场部", "parentId":5 } ], "depPath":".1.2.3.5", "enabled":1, "id":5, "isParent":1, "name":"市场部", "parentId":3},{ "children":[ ], "depPath":".1.2.3.12", "enabled":1, "id":12, "isParent":0, "name":"技术部", "parentId":3},{ "children":[ ], "depPath":".1.2.3.13", "enabled":1, "id":13, "isParent":0, "name":"运维部", "parentId":3} ], "depPath":".1.2.3", "enabled":1, "id":3, "isParent":1, "name":"总办", "parentId":2 } ], "depPath":".1.2", "enabled":1, "id":2, "isParent":1, "name":"董事会", "parentId":1 } ], "depPath":".1", "enabled":1, "id":1, "isParent":1, "name":"股东会", "parentId":-1 }]2.方式2:
方式2是通过java的递归查询实现
代码如下（示例）：
@Override public List<Department> getAll2() {// 查询全部部门 List<Department> list = departmentMapper.selectList(null);// 获取根节点 List<Department> Departments = list.stream() .filter(e -> e.getParentId()==-1) .map(e -> { e.setChildren(getChildrens(e, list)); return e; }).collect(Collectors.toList()); return Departments; } private List<Department> getChildrens(Department e, List<Department> list) { List<Department> children = list.stream() .filter(m -> Objects.equals(e.getId(), m.getParentId())) .map(m -> { m.setChildren(getChildrens(m, list)); return m; }).collect(Collectors.toList()); return children; }测试结果同上：
@Test public void testGetDepartments2(){ List<Department> list = departmentService.getAll2(); System.out.println(JSON.toJSONString(list)); }
笔者推荐第二种方式，数据库只查询一次。
总结
来源地址：https://blog.csdn.net/weixin_36870769/article/details/128638316
