由于博主太菜，就直接上图了，结果是正确的。

1：首先看下数据库

2：对应的实体类

3：mapper.xml和mapper.java

再xml中根据限定条件查询出当前所有的部门集合

4：在serviceImpl中做逻辑处理，最后用递归求出结果。

public class PostTotalNumServiceImpl implements PostTotalNumService {

/**

* 根据部门ID获取该部门及其下属部门的ID集合

*/

public List getDeptIdList(String deptId) {

Department department = this.getDepartment(deptId);

List deptIdList = new ArrayList<>();

if (department != null) {

deptIdList.add(department.getId());

deptIdList = addDeptIdList(deptIdList, department);

}

return deptIdList;

}

/**

* 根据部门ID获取该部门及其下属部门树

*/

public Department getDepartment(String deptId) {

List departments = departmentMapper.findAllDepartments();

Map map = departments.stream().collect(

Collectors.toMap(Department::getId, department -> department));

for (Department dept : map.values()) {

Department parent = map.get(dept.getPid());

if (parent != null) {

List children = parent.getChildren() == null ? new ArrayList<>() : parent.getChildren();

children.add(dept);

parent.setChildren(children);

}

}

return map.get(deptId);

}

public List addDeptIdList(List deptIdList, Department department) {

List children = department.getChildren();

if (children != null) {

for (Department d : children) {

deptIdList.add(d.getId());

addDeptIdList(deptIdList, d);

}

}

return deptIdList;

}

}

5：service接口

public interface PostTotalNumService {

/**

*查出当前部门和下属部门的集合

*/

List deptList(String pkDept);

}

6：junit单元测试

public class PostTest extends BaseTest {

@Autowired

private PostTotalNumService postService;

@Test

public void postTest(){

//查询当前部门及下属部门的集合

List strings = postService.deptList("1001K31000000003M1BT");

System.out.println(strings.size());

}

}