Spring Framework

@Component
public class MessageService {
    
    public String getMessage() {
        return "Hello from Spring!";
    }
}

@RestController
public class HelloController {
    
    @Autowired
    private MessageService messageService;
    
    @GetMapping("/hello")
    public String hello() {
        return messageService.getMessage();
    }
}

@Service
public class UserService {
    
    private final UserRepository userRepository;
    
    // Constructor injection (recommended)
    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    
    public User findUserById(Long id) {
        return userRepository.findById(id)
            .orElseThrow(() -> new UserNotFoundException(id));
    }
}

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByLastName(String lastName);
}

@SpringBootApplication
public class MyApplication {
    
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}

@Configuration
public class DatabaseConfig {
    
    @Bean
    @ConfigurationProperties("app.datasource")
    public DataSource dataSource() {
        return new HikariDataSource();
    }
    
    @Bean
    public JdbcTemplate jdbcTemplate(DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }
}