Example of implementing create, read, update, and delete operations using Spring Boot.

Below is an example code implementing CRUD operations using Spring Boot.

1. Firstly, create a entity class, such as User.java:

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String name;
    private int age;
    private String email;

    // getters and setters
}

1. Create a Repository interface, such as UserRepository.java.

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

1. Create a Service class, for example UserService.java:

@Service
public class UserService {
    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

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

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

    public User createUser(User user) {
        return userRepository.save(user);
    }

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

    public User updateUser(Long id, User user) {
        User existingUser = userRepository.findById(id).orElse(null);
        if (existingUser != null) {
            existingUser.setName(user.getName());
            existingUser.setAge(user.getAge());
            existingUser.setEmail(user.getEmail());
            return userRepository.save(existingUser);
        } else {
            return null;
        }
    }
}

1. Create a Controller class, for example UserController.java:

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

    public UserController(UserService userService) {
        this.userService = userService;
    }

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

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

    @PostMapping("/")
    public User createUser(@RequestBody User user) {
        return userService.createUser(user);
    }

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

    @PutMapping("/{id}")
    public User updateUser(@PathVariable Long id, @RequestBody User user) {
        return userService.updateUser(id, user);
    }
}

1. Add the annotation @SpringBootApplication to the main class of the Spring Boot application, and then run the application.

Now, you can use the following API for CRUD operations.

1. Get all users: GET /users/
2. Retrieve specific user: GET /users/{id}
3. Create user: POST request to /users/
4. Remove user: DELETE /users/{id}
5. Update user: PUT request to /users/{id}

Please note that the above code is just an example and you can make appropriate modifications based on your specific requirements.