Spring 프레임워크의 인기와 그 기능 및 장점 탐색

public interface MessageService {
    String getMessage();
}

public class EmailService implements MessageService {
    public String getMessage() {
        return "Email Service";
    }
}

public class SMSService implements MessageService {
    public String getMessage() {
        return "SMS Service";
    }
}

public class MessagePrinter {
    private MessageService service;

    public MessagePrinter(MessageService service) {
        this.service = service;
    }

    public void printMessage() {
        System.out.println(service.getMessage());
    }
}

public class Main {
    public static void main(String[] args) {
        MessageService emailService = new EmailService();
        MessagePrinter emailPrinter = new MessagePrinter(emailService);
        emailPrinter.printMessage();
        
        MessageService smsService = new SMSService();
        MessagePrinter smsPrinter = new MessagePrinter(smsService);
        smsPrinter.printMessage();
    }
}

public interface AccountService {
    void transferMoney(String fromAccountId, String toAccountId, double amount);
}

public class AccountServiceImpl implements AccountService {
    private AccountDAO accountDAO;

    public void setAccountDAO(AccountDAO accountDAO) {
        this.accountDAO = accountDAO;
    }

    @Transactional
    public void transferMoney(String fromAccountId, String toAccountId, double amount) {
        Account fromAccount = accountDAO.getAccountById(fromAccountId);
        Account toAccount = accountDAO.getAccountById(toAccountId);

        fromAccount.setBalance(fromAccount.getBalance() - amount);
        toAccount.setBalance(toAccount.getBalance() + amount);

        accountDAO.updateAccount(fromAccount);
        accountDAO.updateAccount(toAccount);
    }
}

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

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

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

    // other methods...
}

@Service
public class UserService {
    private UserRepository userRepository;

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

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

    // other methods...
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    // custom queries...
}

@Configuration
@EnableWebMvc
@EnableJpaRepositories(basePackages = "com.example.repository")
@EntityScan(basePackages = "com.example.entity")
public class AppConfig implements WebMvcConfigurer {
    // configuration...
}