stream实现递归封装

@Test
void testToTree() {
    Consumer<Object> test = o -> {
        List<Student> studentTree = Steam
                .of(
                        Student.builder().id(1L).name("dromara").build(),
                        Student.builder().id(2L).name("baomidou").build(),
                        Student.builder().id(3L).name("hutool").parentId(1L).build(),
                        Student.builder().id(4L).name("sa-token").parentId(1L).build(),
                        Student.builder().id(5L).name("mybatis-plus").parentId(2L).build(),
                        Student.builder().id(6L).name("looly").parentId(3L).build(),
                        Student.builder().id(7L).name("click33").parentId(4L).build(),
                        Student.builder().id(8L).name("jobob").parentId(5L).build()
                )
                // just 3 lambda,top parentId is null
                .toTree(Student::getId, Student::getParentId, Student::setChildren);
        Assertions.assertEquals(asList(
                Student.builder().id(1L).name("dromara")
                        .children(asList(
                                Student.builder().id(3L).name("hutool").parentId(1L)
                                    .children(singletonList(Student.builder().id(6L).name("looly").parentId(3L).build()))
                                    .build(),
                                Student.builder().id(4L).name("sa-token").parentId(1L)
                                    .children(singletonList(Student.builder().id(7L).name("click33").parentId(4L).build()))
                                    .build()))
                        .build(),
                Student.builder().id(2L).name("baomidou")
                        .children(singletonList(
                                Student.builder().id(5L).name("mybatis-plus").parentId(2L)
                                        .children(singletonList(
                                                Student.builder().id(8L).name("jobob").parentId(5L).build()
                                        ))
                                        .build()))
                        .build()
        ), studentTree);
    };
    test = test.andThen(o -> {
        List<Student> studentTree = Steam
                .of(
                        Student.builder().id(1L).name("dromara").matchParent(true).build(),
                        Student.builder().id(2L).name("baomidou").matchParent(true).build(),
                        Student.builder().id(3L).name("hutool").parentId(1L).build(),
                        Student.builder().id(4L).name("sa-token").parentId(1L).build(),
                        Student.builder().id(5L).name("mybatis-plus").parentId(2L).build(),
                        Student.builder().id(6L).name("looly").parentId(3L).build(),
                        Student.builder().id(7L).name("click33").parentId(4L).build(),
                        Student.builder().id(8L).name("jobob").parentId(5L).build()
                )
                // just 4 lambda ,top by condition
                .toTree(Student::getId, Student::getParentId, Student::setChildren, Student::getMatchParent);
        Assertions.assertEquals(asList(
                Student.builder().id(1L).name("dromara").matchParent(true)
                        .children(asList(
                                Student.builder().id(3L).name("hutool").parentId(1L)
                                        .children(singletonList(Student.builder().id(6L).name("looly").parentId(3L).build()))
                                        .build(),
                                Student.builder().id(4L).name("sa-token").parentId(1L)
                                        .children(singletonList(Student.builder().id(7L).name("click33").parentId(4L).build()))
                                        .build()))
                        .build(),
                Student.builder().id(2L).name("baomidou").matchParent(true)
                        .children(singletonList(
                                Student.builder().id(5L).name("mybatis-plus").parentId(2L)
                                        .children(singletonList(
                                                Student.builder().id(8L).name("jobob").parentId(5L).build()
                                        ))
                                        .build()))
                        .build()
        ), studentTree);
    });
    test.accept(new Object());
}

@Test
void testFlatTree() {
    List<Student> studentTree = asList(
            Student.builder().id(1L).name("dromara")
                    .children(asList(Student.builder().id(3L).name("hutool").parentId(1L)
                                    .children(singletonList(Student.builder().id(6L).name("looly").parentId(3L).build()))
                                    .build(),
                            Student.builder().id(4L).name("sa-token").parentId(1L)
                                    .children(singletonList(Student.builder().id(7L).name("click33").parentId(4L).build()))
                                    .build()))
                    .build(),
            Student.builder().id(2L).name("baomidou")
                    .children(singletonList(
                            Student.builder().id(5L).name("mybatis-plus").parentId(2L)
                                    .children(singletonList(
                                            Student.builder().id(8L).name("jobob").parentId(5L).build()
                                    ))
                                    .build()))
                    .build()
    );
    Assertions.assertEquals(asList(
            Student.builder().id(1L).name("dromara").build(),
            Student.builder().id(2L).name("baomidou").build(),
            Student.builder().id(3L).name("hutool").parentId(1L).build(),
            Student.builder().id(4L).name("sa-token").parentId(1L).build(),
            Student.builder().id(5L).name("mybatis-plus").parentId(2L).build(),
            Student.builder().id(6L).name("looly").parentId(3L).build(),
            Student.builder().id(7L).name("click33").parentId(4L).build(),
            Student.builder().id(8L).name("jobob").parentId(5L).build()
    ), Steam.of(studentTree).flatTree(Student::getChildren, Student::setChildren).sorted(Comparator.comparingLong(Student::getId)).toList());

}

@Data
@Builder
public static class Student {
    @Tolerate
    public Student() {
        // this is an accessible parameterless constructor.
    }

    private String name;
    private Integer age;
    private Long id;
    private Long parentId;
    private List<Student> children;
    private Boolean matchParent;
}