springboot树形结构示例

以下是一个使用Spring Boot实现树形结构的示例：

1. 定义实体类

@Entity
@Table(name = "category")
public class Category {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parent_id")
    private Category parent;

    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, orphanRemoval = true)
    private Set<Category> children = new HashSet<>();

    // constructors, getters and setters
}

2. 定义Repository接口

@Repository
public interface CategoryRepository extends JpaRepository<Category, Long> {
    List<Category> findByParentIsNull();
}

3. 定义Service接口和实现类

@Service
public interface CategoryService {
    List<Category> getAllCategories();
}

@Service
public class CategoryServiceImpl implements CategoryService {
    @Autowired
    private CategoryRepository categoryRepository;

    @Override
    public List<Category> getAllCategories() {
        List<Category> categories = categoryRepository.findByParentIsNull();
        for (Category category : categories) {
            fetchChildren(category);
        }
        return categories;
    }

    private void fetchChildren(Category category) {
        Set<Category> children = category.getChildren();
        if (!children.isEmpty()) {
            for (Category child : children) {
                fetchChildren(child);
            }
        }
    }
}

4. 定义Controller类

@RestController
@RequestMapping("/categories")
public class CategoryController {
    @Autowired
    private CategoryService categoryService;

    @GetMapping
    public List<Category> getAllCategories() {
        return categoryService.getAllCategories();
    }
}

这个示例中，我们使用了一个自关联的实体类Category来表示树形结构，通过Category的parent和children属性来维护父子关系。在CategoryRepository中，我们定义了一个findByParentIsNull方法来获取所有的根节点。在CategoryServiceImpl中，我们通过递归的方式来获取所有的子节点，并将它们作为树形结构返回给Controller。最后，在CategoryController中，我们将树形结构返回给客户端。