java 实现部门层级树

要实现部门层级树，可以使用树形数据结构。以下是一个简单的 Java 实现示例：

首先，需要定义一个部门类，包含部门 ID、父部门 ID、部门名称等属性：

public class Department {
    private int id;
    private int parentId;
    private String name;

    // 构造方法、getter、setter 略
}

接下来，可以定义一个方法，接收部门列表作为参数，返回一个根据部门层级关系构建的树形结构：

public static List<Department> buildDepartmentTree(List<Department> departmentList) {
    // 首先，将所有部门按照父部门 ID 分组
    Map<Integer, List<Department>> departmentMap = departmentList.stream()
            .collect(Collectors.groupingBy(Department::getParentId));

    // 然后，递归构建树形结构
    List<Department> rootDepartments = departmentMap.get(0);
    for (Department department : rootDepartments) {
        buildDepartmentTree(department, departmentMap);
    }
    return rootDepartments;
}

private static void buildDepartmentTree(Department department, Map<Integer, List<Department>> departmentMap) {
    List<Department> subDepartments = departmentMap.get(department.getId());
    if (subDepartments != null) {
        department.setSubDepartments(subDepartments);
        for (Department subDepartment : subDepartments) {
            buildDepartmentTree(subDepartment, departmentMap);
        }
    }
}

上述代码中，首先将所有部门按照父部门 ID 分组，然后从根节点开始递归构建树形结构，直到所有节点都被加入到树中。

最后，可以通过递归遍历树形结构，将部门层级树打印出来：

public static void printDepartmentTree(List<Department> departmentList, int level) {
    if (departmentList == null || departmentList.isEmpty()) {
        return;
    }
    for (Department department : departmentList) {
        System.out.println(String.join("", Collections.nCopies(level, "-"))
                + department.getName() + " (" + department.getId() + ")");
        printDepartmentTree(department.getSubDepartments(), level + 1);
    }
}

这样，就可以通过以下代码来构建和打印部门层级树：

List<Department> departmentList = Arrays.asList(
        new Department(1, 0, "总公司"),
        new Department(2, 1, "财务部"),
        new Department(3, 1, "人力资源部"),
        new Department(4, 2, "财务一部"),
        new Department(5, 2, "财务二部"),
        new Department(6, 3, "招聘组"),
        new Department(7, 3, "培训组")
);
List<Department> departmentTree = buildDepartmentTree(departmentList);
printDepartmentTree(departmentTree, 0);

输出结果如下：

总公司 (1)
-财务部 (2)
--财务一部 (4)
--财务二部 (5)
-人力资源部 (3)
--招聘组 (6)
--培训组 (7)