Folder aFolder = new Folder();
		aFolder.setName("folder a").setParent(null);

		Folder bFolder = new Folder();
		bFolder.setName("folder b");

		BookMark aBookMark = new BookMark();
		aBookMark.setUrl("www.naver.com").setName("bookmark a");


		BookMark bBookMark = new BookMark();
		bBookMark.setUrl("www.daum.net").setName("bookmark b");

		BookMark cBookMark = new BookMark();
		cBookMark.setUrl("www.google.com").setName("bookmark c");

		aFolder.addChildren(bFolder, aBookMark);
		bFolder.addChildren(bBookMark, cBookMark);

		em.persist(aFolder);
		em.persist(bFolder);

		em.persist(aBookMark);
		em.persist(bBookMark);
		em.persist(cBookMark);

		long rootFileId = aFolder.getId();
		em.flush();
		em.clear();

		// 모든 폴더 찾아내기
		File findRootFile = em.find(File.class, rootFileId);

		out.println("findFolder = " + findRootFile);

		Queue<File> queue = new LinkedList<>();
		queue.offer(findRootFile);

		while (!queue.isEmpty()) {
			File pollFile = queue.poll();
			out.println("pollFile.getName() = " + pollFile.getName());
			if (pollFile instanceof Folder) {
				Folder pollFolder = (Folder)pollFile;
				List<File> pollChildren = pollFolder.getChildren();
				pollChildren.forEach(queue::offer);
			}
		}

		em.remove(findRootFile);

@Entity
@SequenceGenerator(
	name = "FILE_SEQ_GEN",
	sequenceName = "FILE_SEQ",
	initialValue = 1
)
@Getter
@DiscriminatorColumn
@Inheritance(strategy = InheritanceType.JOINED)
@NoArgsConstructor(access = AccessLevel.PROTECTED)
@AllArgsConstructor(access = AccessLevel.PROTECTED)
public class File extends BaseEntity {

	@Id
	@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "FILE_SEQ_GEN")
	private long id;

	private String name;

	@JoinColumn(name = "PARENT_ID")
	@ManyToOne(fetch = FetchType.LAZY)
	private File parent;

	public File setName(String name) {
		this.name = name;
		return this;
	}

	public File setParent(File parent) {
		this.parent = parent;
		return this;
	}
}

@Entity
@Getter @Setter
public class Folder extends File {

	@BatchSize(size = 900)
	@OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, orphanRemoval = true)
	private List<File> children = new ArrayList<>();

	public Folder addChildren(File... files) {
		this.children.addAll(Arrays.asList(files));
		Arrays.stream(files).forEach(file -> file.setParent(this));
		return this;
	}

	@Override
	public String toString() {
		return "Folder{}";
	}
}

@Entity
@Getter
public class BookMark extends File {

	private String url;

	public BookMark setUrl(String url) {
		this.url = url;
		return this;
	}

	@Override
	public String toString() {
		return "BookMark{}";
	}
}

aFolder.addChildren(bFolder, aBookMark);