Quiz: Beans and Spring Context

Test your knowledge on beans and the application context.

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

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Questions 1-15: Beans

Question 1: What is a Spring bean?

Answer: A bean is an object managed by the Spring IoC container:

• Created and configured by Spring
• Automatic dependency injection
• Managed lifecycle
• Singleton by default

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Question 2: How to declare a bean with an annotation?

Answer:

// With stereotype (automatic scan)
@Component
public class MyService { }

@Service
public class UserService { }

@Repository
public class UserRepository { }

@Controller
public class UserController { }

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Question 3: How to declare a bean with @Bean?

Answer:

@Configuration
public class AppConfig {
    
    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
    
    @Bean
    public ObjectMapper objectMapper() {
        return new ObjectMapper()
            .registerModule(new JavaTimeModule());
    }
}

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Question 4: What is the difference between @Component and @Bean?

Answer:

@Component	@Bean
On a class	On a method
Auto-detected by scan	Explicitly declared
Classes you control	Third-party classes
Limited configuration	Full control

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Question 5: What is the default name of a bean?

Answer: The class name in camelCase:

@Component
public class UserService { }
// Name: userService

@Bean
public RestTemplate myRestTemplate() { }
// Name: myRestTemplate

Customize:

@Component("customName")
@Bean("customName")

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Question 6: How to retrieve a bean by its name?

Answer:

@Autowired
private ApplicationContext context;

public void example() {
    UserService service = context.getBean("userService", UserService.class);
    
    // Or by type
    UserService service = context.getBean(UserService.class);
}

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Question 7: What is the lifecycle of a bean?

Answer:

1. Instantiation: object creation
2. Injection: dependency injection
3. Initialization: @PostConstruct methods
4. Usage: bean ready
5. Destruction: @PreDestroy methods

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Question 8: How to execute code after initialization?

Answer:

@Component
public class DataLoader {
    
    @PostConstruct
    public void init() {
        log.info("Bean initialized");
        loadData();
    }
}

// Or with @Bean
@Bean(initMethod = "init")
public MyService myService() { }

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Question 9: How to execute code before destruction?

Answer:

@Component
public class ResourceManager {
    
    @PreDestroy
    public void cleanup() {
        log.info("Cleaning up resources");
        closeConnections();
    }
}

// Or with @Bean
@Bean(destroyMethod = "close")
public DataSource dataSource() { }

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Question 10: What are InitializingBean and DisposableBean?

Answer: Alternative interfaces for the lifecycle:

@Component
public class MyBean implements InitializingBean, DisposableBean {
    
    @Override
    public void afterPropertiesSet() {
        // After injection
    }
    
    @Override
    public void destroy() {
        // Before destruction
    }
}

Prefer @PostConstruct/@PreDestroy for less coupling.

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Question 11: How to implement ApplicationRunner?

Answer:

@Component
public class StartupRunner implements ApplicationRunner {
    
    @Override
    public void run(ApplicationArguments args) {
        log.info("Application started");
        // Arguments: args.getOptionValues("config")
    }
}

Executed after the full context startup.

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Question 12: How to implement CommandLineRunner?

Answer:

@Component
public class DataInitializer implements CommandLineRunner {
    
    private final UserRepository repository;
    
    @Override
    public void run(String... args) {
        repository.save(new User("Admin"));
        log.info("Data initialized");
    }
}

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Question 13: How to order the execution of runners?

Answer:

@Component
@Order(1)
public class FirstRunner implements CommandLineRunner { }

@Component
@Order(2)
public class SecondRunner implements CommandLineRunner { }

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Question 14: How to create a conditional bean?

Answer:

@Bean
@ConditionalOnProperty(name = "cache.enabled", havingValue = "true")
public CacheManager cacheManager() { }

@Bean
@ConditionalOnMissingBean(DataSource.class)
public DataSource defaultDataSource() { }

@Bean
@Profile("dev")
public DevService devService() { }

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Question 15: What is @Lazy?

Answer: Delays the creation of the bean until first access:

@Component
@Lazy
public class HeavyService {
    public HeavyService() {
        // Called only on first access
    }
}

// Or at injection
public MyController(@Lazy HeavyService service) { }

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Questions 16-30: Context and Scopes

Question 16: What is the ApplicationContext?

Answer: The central Spring container that:

• Manages all beans
• Provides dependency injection
• Publishes events
• Loads resources
• Manages internationalization

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Question 17: What are the available bean scopes?

Answer:

Scope	Description
singleton	One instance per context (default)
prototype	New instance for each request
request	One instance per HTTP request
session	One instance per HTTP session
application	One instance per ServletContext

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Question 18: How to define the scope of a bean?

Answer:

@Component
@Scope("prototype")
public class PrototypeBean { }

@Bean
@Scope("request")
public RequestContext requestContext() { }

// Or with constants
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)

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Question 19: What problem arises when injecting a prototype into a singleton?

Answer: The singleton always keeps the same instance of the prototype:

@Component  // Singleton
public class SingletonService {
    
    private final PrototypeBean proto;  // Always the same instance!
    
    public SingletonService(PrototypeBean proto) {
        this.proto = proto;
    }
}

Solution: use ObjectProvider or @Lookup.

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Question 20: How to use ObjectProvider?

Answer:

@Component
public class SingletonService {
    
    private final ObjectProvider<PrototypeBean> protoProvider;
    
    public void doWork() {
        PrototypeBean proto = protoProvider.getObject();  // New instance
    }
}

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Question 21: How to use @Lookup?

Answer:

@Component
public abstract class SingletonService {
    
    @Lookup
    protected abstract PrototypeBean getPrototype();
    
    public void doWork() {
        PrototypeBean proto = getPrototype();  // New instance
    }
}

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Question 22: How to listen to context events?

Answer:

@Component
public class ContextListener {
    
    @EventListener
    public void onContextRefreshed(ContextRefreshedEvent event) {
        log.info("Context refreshed");
    }
    
    @EventListener
    public void onContextClosed(ContextClosedEvent event) {
        log.info("Context closed");
    }
}

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Question 23: How to publish a custom event?

Answer:

// Event
public class UserCreatedEvent extends ApplicationEvent {
    private final User user;
    
    public UserCreatedEvent(Object source, User user) {
        super(source);
        this.user = user;
    }
}

// Publishing
@Service
public class UserService {
    
    private final ApplicationEventPublisher publisher;
    
    public void createUser(User user) {
        userRepository.save(user);
        publisher.publishEvent(new UserCreatedEvent(this, user));
    }
}

// Listening
@Component
public class UserEventListener {
    
    @EventListener
    public void onUserCreated(UserCreatedEvent event) {
        log.info("User created: {}", event.getUser().getName());
    }
}

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Question 24: How to listen to an event asynchronously?

Answer:

@EnableAsync
@Configuration
public class AsyncConfig { }

@Component
public class AsyncListener {
    
    @Async
    @EventListener
    public void onEvent(MyEvent event) {
        // Executed in another thread
    }
}

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Question 25: How to access the Spring environment?

Answer:

@Component
public class ConfigService {
    
    private final Environment env;
    
    public ConfigService(Environment env) {
        this.env = env;
    }
    
    public void showConfig() {
        String property = env.getProperty("app.name");
        String[] profiles = env.getActiveProfiles();
        boolean isDev = env.acceptsProfiles(Profiles.of("dev"));
    }
}

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Question 26: How to load external resources?

Answer:

@Component
public class ResourceLoader {
    
    @Value("classpath:data/config.json")
    private Resource configResource;
    
    public void load() throws IOException {
        String content = new String(configResource.getInputStream().readAllBytes());
    }
}

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Question 27: How to implement EnvironmentPostProcessor?

Answer:

public class CustomEnvProcessor implements EnvironmentPostProcessor {
    
    @Override
    public void postProcessEnvironment(ConfigurableEnvironment env, SpringApplication app) {
        // Modify the environment before startup
        Map<String, Object> props = new HashMap<>();
        props.put("custom.property", "value");
        env.getPropertySources().addFirst(new MapPropertySource("custom", props));
    }
}

Register in META-INF/spring.factories.

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Question 28: How to use Spring profiles?

Answer:

// Bean active only in dev
@Component
@Profile("dev")
public class DevOnlyService { }

// Bean active except in prod
@Component
@Profile("!prod")
public class NonProdService { }

// Multiple profiles
@Component
@Profile({"dev", "test"})
public class DevTestService { }

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Question 29: How to define beans in separate configurations?

Answer:

@Configuration
public class DatabaseConfig {
    @Bean
    public DataSource dataSource() { }
}

@Configuration
public class SecurityConfig {
    @Bean
    public SecurityFilterChain filterChain() { }
}

@Configuration
@Import({DatabaseConfig.class, SecurityConfig.class})
public class AppConfig { }

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Question 30: How to test a Spring context?

Answer:

@SpringBootTest
class ContextTest {
    
    @Autowired
    private ApplicationContext context;
    
    @Test
    void contextLoads() {
        assertThat(context).isNotNull();
        assertThat(context.getBean(UserService.class)).isNotNull();
    }
    
    @Test
    void beanExists() {
        assertThat(context.containsBean("userService")).isTrue();
    }
}

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Score

Score	Level
27-30	Excellent - Mastered beans and context
21-26	Good - Some revisions needed
15-20	Average - Review the chapter
Less than 15	Needs review

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