用springboot写增删改查功能

好的，下面是一个简单的示例：

1. 创建一个实体类

@Entity
@Table(name = "user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private Integer age;

    // getter/setter 省略
}

2. 创建一个 DAO 层接口

public interface UserRepository extends JpaRepository<User, Long> {
}

3. 创建一个 Service 层接口

public interface UserService {
    List<User> findAll();
    User findById(Long id);
    void save(User user);
    void deleteById(Long id);
}

4. 实现 Service 层接口

@Service
public class UserServiceImpl implements UserService {
    @Autowired
    private UserRepository userRepository;

    @Override
    public List<User> findAll() {
        return userRepository.findAll();
    }

    @Override
    public User findById(Long id) {
        return userRepository.findById(id).orElse(null);
    }

    @Override
    public void save(User user) {
        userRepository.save(user);
    }

    @Override
    public void deleteById(Long id) {
        userRepository.deleteById(id);
    }
}

5. 创建一个 Controller 类

@RestController
@RequestMapping("/users")
public class UserController {
    @Autowired
    private UserService userService;

    @GetMapping("")
    public List<User> getAllUsers() {
        return userService.findAll();
    }

    @GetMapping("/{id}")
    public User getUserById(@PathVariable Long id) {
        return userService.findById(id);
    }

    @PostMapping("")
    public void createUser(@RequestBody User user) {
        userService.save(user);
    }

    @PutMapping("/{id}")
    public void updateUser(@PathVariable Long id, @RequestBody User user) {
        User oldUser = userService.findById(id);
        if (oldUser != null) {
            oldUser.setName(user.getName());
            oldUser.setAge(user.getAge());
            userService.save(oldUser);
        }
    }

    @DeleteMapping("/{id}")
    public void deleteUser(@PathVariable Long id) {
        userService.deleteById(id);
    }
}

6. 启动应用程序，使用 Postman 或其他工具测试增删改查功能。