Quiz: Advanced Techniques

Test your knowledge on WebFlux, Redis, RabbitMQ, Scheduling, and WebSockets.

30 questions - Click on each question to reveal the answer.

Questions 1-10: Reactive Programming (WebFlux)

Question 1: What is the difference between Spring MVC and WebFlux?

Answer:

Spring MVC	WebFlux
Blocking	Non-blocking
1 thread/request	Event loop
Servlet API	Reactive Streams
Tomcat, Jetty	Netty
Vertical scalability	Horizontal scalability

Question 2: What is the difference between Mono and Flux?

Answer:

Mono: 0 or 1 element
Flux: 0 to N elements

Mono<User> user = userRepository.findById(1L);
Flux<User> users = userRepository.findAll();

Question 3: What are common Mono/Flux operators?

Answer:

Operator	Description
`map`	Synchronous transformation
`flatMap`	Async transformation
`filter`	Filtering
`zip`	Combine
`onErrorReturn`	Error fallback
`switchIfEmpty`	Empty fallback
`timeout`	Time limit
`retry`	Retry

Question 4: How to write a reactive controller?

Answer:

@RestController
@RequestMapping("/api/users")
public class UserController {
    
    private final UserRepository repository;
    
    @GetMapping
    public Flux<User> getAll() {
        return repository.findAll();
    }
    
    @GetMapping("/{id}")
    public Mono<ResponseEntity<User>> getById(@PathVariable Long id) {
        return repository.findById(id)
            .map(ResponseEntity::ok)
            .defaultIfEmpty(ResponseEntity.notFound().build());
    }
    
    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public Mono<User> create(@RequestBody User user) {
        return repository.save(user);
    }
}

Question 5: What is R2DBC?

Answer: Reactive Relational Database Connectivity - non-blocking access to relational databases.

public interface UserRepository extends ReactiveCrudRepository<User, Long> {
    Flux<User> findByEmail(String email);
}

Replaces blocking JPA/JDBC in reactive applications.

Question 6: How to use WebClient?

Answer:

@Service
public class ExternalApiService {
    
    private final WebClient webClient;
    
    public Mono<Data> fetchData(String id) {
        return webClient.get()
            .uri("/data/{id}", id)
            .retrieve()
            .bodyToMono(Data.class)
            .timeout(Duration.ofSeconds(5))
            .retry(3);
    }
}

Question 7: Why never call block() in production?

Answer: block() blocks the thread, negating the benefits of reactive:

Blocks the event loop
Reduces throughput
Can cause deadlocks

Use only in tests.

Question 8: How to test reactive code?

Answer:

@Test
void shouldFindUser() {
    Mono<User> userMono = userService.findById(1L);
    
    StepVerifier.create(userMono)
        .assertNext(user -> {
            assertThat(user.getName()).isEqualTo("John");
        })
        .verifyComplete();
}

@Test
void shouldHandleError() {
    Mono<User> userMono = userService.findById(999L);
    
    StepVerifier.create(userMono)
        .expectError(NotFoundException.class)
        .verify();
}

Question 9: When to use WebFlux?

Answer:

High concurrency (thousands of connections)
Data streaming
Real-time applications
Integrations with many external calls

Avoid if: untrained team, blocking libraries, simple CRUD.

Question 10: How to handle errors reactively?

Answer:

return userRepository.findById(id)
    .switchIfEmpty(Mono.error(new NotFoundException("User not found")))
    .onErrorReturn(new User("Fallback"))
    .onErrorResume(e -> {
        log.error("Error: {}", e.getMessage());
        return Mono.empty();
    });

Questions 11-17: Caching with Redis

Question 11: How to configure Spring Cache with Redis?

Answer:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-cache</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>

@Configuration
@EnableCaching
public class CacheConfig { }

Question 12: How to use @Cacheable?

Answer:

@Cacheable(value = "users", key = "#id")
public User findById(Long id) {
    log.info("Fetching from DB");
    return userRepository.findById(id).orElseThrow();
}

// First call: DB
// Subsequent calls: cache

Question 13: What is the difference between @Cacheable, @CachePut, and @CacheEvict?

Answer:

Annotation	Behavior
`@Cacheable`	Reads from cache or executes and caches
`@CachePut`	Always executes and updates the cache
`@CacheEvict`	Removes from cache

@CachePut(value = "users", key = "#user.id")
public User update(User user) { }

@CacheEvict(value = "users", key = "#id")
public void delete(Long id) { }

@CacheEvict(value = "users", allEntries = true)
public void clearCache() { }

Question 14: How to configure cache TTL?

Answer:

@Bean
public RedisCacheManager cacheManager(RedisConnectionFactory factory) {
    RedisCacheConfiguration config = RedisCacheConfiguration.defaultCacheConfig()
        .entryTtl(Duration.ofMinutes(30))
        .disableCachingNullValues();
    
    return RedisCacheManager.builder(factory)
        .cacheDefaults(config)
        .build();
}

Question 15: How to use RedisTemplate directly?

Answer:

@Service
public class SessionService {
    
    private final RedisTemplate<String, Object> redisTemplate;
    
    public void saveSession(String token, UserSession session) {
        redisTemplate.opsForValue().set(
            "session:" + token, 
            session, 
            Duration.ofHours(1)
        );
    }
    
    public UserSession getSession(String token) {
        return (UserSession) redisTemplate.opsForValue()
            .get("session:" + token);
    }
}

Question 16: How to handle Redis unavailability?

Answer:

@Configuration
public class CacheConfig extends CachingConfigurerSupport {
    
    @Override
    public CacheErrorHandler errorHandler() {
        return new SimpleCacheErrorHandler() {
            @Override
            public void handleCacheGetError(RuntimeException ex, Cache cache, Object key) {
                log.warn("Cache error: {}", ex.getMessage());
                // Continue without cache
            }
        };
    }
}

Question 17: When to cache?

Answer:

Frequently read, rarely modified data
Expensive computations
External API calls
Reference data (countries, categories)

Avoid: real-time data, sensitive personal data.

Questions 18-23: Messaging with RabbitMQ

Question 18: How to configure RabbitMQ with Spring?

Answer:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-amqp</artifactId>
</dependency>

spring:
  rabbitmq:
    host: localhost
    port: 5672
    username: guest
    password: guest

Question 19: What are the types of RabbitMQ exchanges?

Answer:

Type	Routing
Direct	Exact routing key
Fanout	Broadcast to all queues
Topic	Pattern matching (*.error, order.#)
Headers	Based on headers

Question 20: How to send a message?

Answer:

@Service
public class OrderProducer {
    
    private final RabbitTemplate rabbitTemplate;
    
    public void sendOrderEvent(OrderEvent event) {
        rabbitTemplate.convertAndSend(
            "order.exchange",  // exchange
            "order.created",   // routing key
            event              // message
        );
    }
}

Question 21: How to receive a message?

Answer:

@Component
public class OrderListener {
    
    @RabbitListener(queues = "order.queue")
    public void handleOrder(OrderEvent event) {
        log.info("Received: {}", event);
        processOrder(event);
    }
}

Question 22: What is a Dead Letter Queue?

Answer: Queue that receives failed messages (rejected, expired, max retries):

@Bean
public Queue orderQueue() {
    return QueueBuilder.durable("order.queue")
        .withArgument("x-dead-letter-exchange", "dlx.exchange")
        .withArgument("x-dead-letter-routing-key", "dlq")
        .build();
}

Allows analyzing and reprocessing errors.

Question 23: How to ensure message delivery?

Answer:

Publisher confirms: exchange confirmation
Consumer acks: processing confirmation
Persistent messages: survives restart
Durable queues: persistent queues

@RabbitListener(queues = "order.queue", ackMode = "MANUAL")
public void handle(OrderEvent event, Channel channel, @Header(AmqpHeaders.DELIVERY_TAG) long tag) {
    try {
        process(event);
        channel.basicAck(tag, false);
    } catch (Exception e) {
        channel.basicNack(tag, false, false);
    }
}

Questions 24-27: Scheduled Tasks

Question 24: How to enable scheduling?

Answer:

@SpringBootApplication
@EnableScheduling
public class Application { }

Question 25: What are the options for @Scheduled?

Answer:

// Every 5 seconds
@Scheduled(fixedRate = 5000)

// 5 seconds after completion
@Scheduled(fixedDelay = 5000)

// Cron expression
@Scheduled(cron = "0 0 6 * * *")  // Every day at 6 AM

// With initial delay
@Scheduled(fixedRate = 5000, initialDelay = 10000)

Question 26: How to write a Cron expression?

Answer:

┌───────────── second (0-59)
│ ┌───────────── minute (0-59)
│ │ ┌───────────── hour (0-23)
│ │ │ ┌───────────── day of month (1-31)
│ │ │ │ ┌───────────── month (1-12)
│ │ │ │ │ ┌───────────── day of week (0-7)
* * * * * *

Examples:

0 0 * * * *: every hour
0 0 9 * * MON-FRI: 9 AM on weekdays
0 */15 * * * *: every 15 minutes

Question 27: How to run a method asynchronously?

Answer:

@EnableAsync
@Configuration
public class AsyncConfig { }

@Service
public class EmailService {
    
    @Async
    public CompletableFuture<Boolean> sendEmail(String to) {
        // Executed in another thread
        return CompletableFuture.completedFuture(true);
    }
}

Questions 28-30: WebSockets

Question 28: How to configure WebSocket with STOMP?

Answer:

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
    
    @Override
    public void configureMessageBroker(MessageBrokerRegistry registry) {
        registry.enableSimpleBroker("/topic", "/queue");
        registry.setApplicationDestinationPrefixes("/app");
    }
    
    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/ws").withSockJS();
    }
}

Question 29: How to send and receive WebSocket messages?

Answer:

@Controller
public class ChatController {
    
    @MessageMapping("/chat.send")
    @SendTo("/topic/messages")
    public ChatMessage send(ChatMessage message) {
        return message;
    }
}

// Programmatic sending
@Service
public class NotificationService {
    
    private final SimpMessagingTemplate template;
    
    public void notifyUser(String userId, Notification notif) {
        template.convertAndSendToUser(userId, "/queue/notifications", notif);
    }
}

Question 30: When to use WebSocket vs REST?

Answer:

WebSocket	REST
Bidirectional communication	Request-Response
Real-time	Static data
Chat, notifications	CRUD, API
Persistent connection	Short connections
Games, trading	Traditional applications

Score

Score	Level
27-30	Excellent - Mastered advanced techniques
21-26	Good - Some revisions needed
15-20	Average - Review the chapters
Less than 15	Needs improvement

Back to Module 14

Questions 1-10: Reactive Programming (WebFlux)​

Questions 11-17: Caching with Redis​

Questions 18-23: Messaging with RabbitMQ​

Questions 24-27: Scheduled Tasks​

Questions 28-30: WebSockets​

Score​

Questions 1-10: Reactive Programming (WebFlux)

Questions 11-17: Caching with Redis

Questions 18-23: Messaging with RabbitMQ

Questions 24-27: Scheduled Tasks

Questions 28-30: WebSockets

Score