Quiz: Scopes and Advanced Configuration

Test your knowledge on scopes and configuration properties.

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

Questions 1-15: Scopes

Question 1: What is the default scope of a Spring bean?

Answer: Singleton - a single instance per Spring container.

@Component
public class MyService { }  // Default singleton

Question 2: How to create a prototype bean?

Answer:

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

// Or
@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
public MyService myService() { }

New instance on each lookup.

Question 3: When to use the prototype scope?

Answer:

Objects with mutable state
Non-thread-safe objects
Expensive objects to create but single-use
Independent workflows or processes

Example: file parser, command processor.

Question 4: What is the request scope?

Answer: One instance per HTTP request:

@Component
@Scope(value = WebApplicationContext.SCOPE_REQUEST, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class RequestContext {
    private User currentUser;
    // Request-specific data
}

Destroyed at the end of the request.

Question 5: What is the session scope?

Answer: One instance per HTTP session:

@Component
@Scope(value = WebApplicationContext.SCOPE_SESSION, proxyMode = ScopedProxyMode.TARGET_CLASS)
public class ShoppingCart {
    private List<Item> items = new ArrayList<>();
}

Persists between requests from the same user.

Question 6: Why is proxyMode necessary for request/session?

Answer: The singleton is created at startup, before any request. The proxy allows access to the scoped bean dynamically:

@Component
@Scope(value = "request", proxyMode = ScopedProxyMode.TARGET_CLASS)
public class RequestData { }

@Service  // Singleton
public class MyService {
    private final RequestData data;  // Proxy, not the actual instance
}

Question 7: What are the types of proxyMode?

Answer:

Mode	Usage
`DEFAULT`	No proxy
`NO`	No proxy
`INTERFACES`	JDK proxy (interface)
`TARGET_CLASS`	CGLIB proxy (class)

Use TARGET_CLASS for concrete classes.

Question 8: How to create a custom scope?

Answer:

public class TenantScope implements Scope {
    
    private final ThreadLocal<Map<String, Object>> beans = new ThreadLocal<>();
    
    @Override
    public Object get(String name, ObjectFactory<?> factory) {
        Map<String, Object> scope = beans.get();
        if (!scope.containsKey(name)) {
            scope.put(name, factory.getObject());
        }
        return scope.get(name);
    }
    
    @Override
    public Object remove(String name) {
        return beans.get().remove(name);
    }
    // ...
}

@Configuration
public class ScopeConfig implements BeanFactoryPostProcessor {
    
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory factory) {
        factory.registerScope("tenant", new TenantScope());
    }
}

Question 9: How to manage thread-safety with singletons?

Answer:

Stateless beans (no mutable fields)
Immutable fields (final)
Synchronization if necessary
Use ThreadLocal for per-thread state

@Service
public class StatelessService {
    // No mutable fields
    private final UserRepository repo;  // Immutable
    
    public User process(Long id) {
        // Everything in local variables
        return repo.findById(id).orElseThrow();
    }
}

Question 10: How to check the scope of a bean?

Answer:

@Autowired
private ConfigurableListableBeanFactory beanFactory;

public void checkScope() {
    BeanDefinition definition = beanFactory.getBeanDefinition("myBean");
    String scope = definition.getScope();
    log.info("Scope: {}", scope);  // singleton, prototype, etc.
}

Question 11: How to use @RefreshScope?

Answer: For beans that need to be recreated after a configuration refresh:

@RefreshScope
@Component
public class DynamicConfig {
    
    @Value("${app.feature.enabled}")
    private boolean featureEnabled;
}

After POST /actuator/refresh, the bean is recreated with new values.

Question 12: How to test scoped beans?

Answer:

@SpringBootTest
@WebAppConfiguration  // For request/session scope
class ScopedBeanTest {
    
    @Autowired
    private WebApplicationContext context;
    
    @Test
    void testRequestScope() {
        MockHttpServletRequest request = new MockHttpServletRequest();
        RequestContextHolder.setRequestAttributes(new ServletRequestAttributes(request));
        
        try {
            RequestData data = context.getBean(RequestData.class);
            assertThat(data).isNotNull();
        } finally {
            RequestContextHolder.resetRequestAttributes();
        }
    }
}

Question 13: How are prototype beans destroyed?

Answer: Spring does not automatically destroy prototype beans!

@Component
@Scope("prototype")
public class ExpensiveResource implements DisposableBean {
    
    @Override
    public void destroy() {
        // Never called automatically!
    }
}

Must be managed manually or use a BeanFactoryPostProcessor.

Question 14: How to obtain multiple beans of the same type?

Answer:

// List of all beans
@Autowired
private List<NotificationService> notificationServices;

// Map with name as key
@Autowired
private Map<String, NotificationService> notificationMap;

// ObjectProvider for lazy access
@Autowired
private ObjectProvider<NotificationService> provider;

public void notify() {
    provider.forEach(service -> service.send(message));
}

Question 15: How to use @Primary vs @Qualifier?

Answer:

// @Primary: default bean
@Service
@Primary
public class EmailNotification implements NotificationService { }

@Service
public class SmsNotification implements NotificationService { }

// @Qualifier: explicit choice
public MyController(@Qualifier("smsNotification") NotificationService notif) { }

Questions 16-30: Configuration

Question 16: How to read a property with @Value?

Answer:

@Value("${app.name}")
private String appName;

@Value("${app.timeout:5000}")  // Default value
private int timeout;

@Value("${app.features}")  // List: a,b,c
private List<String> features;

@Value("#{${app.map}}")  // Map: {key1: 'val1', key2: 'val2'}
private Map<String, String> map;

Question 17: How to use SpEL in @Value?

Answer:

@Value("#{systemProperties['user.home']}")
private String userHome;

@Value("#{T(java.lang.Math).random()}")
private double randomValue;

@Value("#{myBean.property}")
private String fromBean;

@Value("#{${app.timeout} * 2}")
private int doubleTimeout;

Question 18: How to group properties with @ConfigurationProperties?

Answer:

# application.yml
app:
  mail:
    host: smtp.example.com
    port: 587
    username: user
    password: secret

@ConfigurationProperties(prefix = "app.mail")
@Validated
public class MailProperties {
    
    @NotBlank
    private String host;
    
    @Min(1)
    @Max(65535)
    private int port;
    
    private String username;
    private String password;
    
    // Getters and setters
}

@Configuration
@EnableConfigurationProperties(MailProperties.class)
public class AppConfig { }

Question 19: How to validate properties?

Answer:

@ConfigurationProperties(prefix = "app")
@Validated
public class AppProperties {
    
    @NotNull
    private String name;
    
    @Min(1000)
    @Max(65535)
    private int port;
    
    @Email
    private String adminEmail;
    
    @Valid  // Validate nested objects
    private DatabaseProperties database;
}

The application fails to start if invalid.

Question 20: How to configure nested objects?

Answer:

app:
  database:
    primary:
      url: jdbc:postgresql://primary/db
      username: user1
    secondary:
      url: jdbc:postgresql://secondary/db
      username: user2

@ConfigurationProperties(prefix = "app.database")
public class DatabaseProperties {
    private DataSourceConfig primary;
    private DataSourceConfig secondary;
    
    public static class DataSourceConfig {
        private String url;
        private String username;
        // Getters/setters
    }
}

Question 21: How to configure lists?

Answer:

app:
  servers:
    - host: server1.example.com
      port: 8080
    - host: server2.example.com
      port: 8081

@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private List<ServerConfig> servers;
    
    public static class ServerConfig {
        private String host;
        private int port;
    }
}

Question 22: How to use configuration profiles?

Answer:

# application.yml (common)
app:
  name: My App

---
# application-dev.yml
spring:
  config:
    activate:
      on-profile: dev
logging:
  level:
    root: DEBUG

---
# application-prod.yml
spring:
  config:
    activate:
      on-profile: prod
logging:
  level:
    root: WARN

Activation:

java -jar app.jar --spring.profiles.active=prod

Question 23: How to externalize configuration?

Answer: Priority order (from highest to lowest):

Command line arguments
Environment variables
External application-\{profile\}.yml
External application.yml
application-\{profile\}.yml inside the JAR
application.yml inside the JAR

java -jar app.jar --server.port=9090
export SERVER_PORT=9090

Question 24: How to load configuration from an external file?

Answer:

# External file
java -jar app.jar --spring.config.location=file:/etc/myapp/config/

# Multiple locations
java -jar app.jar --spring.config.location=classpath:/,file:/config/

# Specific file
java -jar app.jar --spring.config.name=custom

Question 25: How to use environment variables?

Answer:

spring:
  datasource:
    url: ${DB_URL:jdbc:h2:mem:default}
    username: ${DB_USER:sa}
    password: ${DB_PASSWORD:}

Mapping convention:

app.my-property → APP_MY_PROPERTY
. → _
- → _

Question 26: How to encrypt sensitive properties?

Answer: With Jasypt or Spring Cloud Config:

<dependency>
    <groupId>com.github.ulisesbocchio</groupId>
    <artifactId>jasypt-spring-boot-starter</artifactId>
</dependency>

jasypt:
  encryptor:
    password: ${JASYPT_PASSWORD}

spring:
  datasource:
    password: ENC(encrypted_value_here)

Question 27: How to create a custom PropertySource?

Answer:

public class VaultPropertySource extends PropertySource<VaultClient> {
    
    public VaultPropertySource(VaultClient client) {
        super("vault", client);
    }
    
    @Override
    public Object getProperty(String name) {
        if (name.startsWith("vault.")) {
            return source.getSecret(name.substring(6));
        }
        return null;
    }
}

@Configuration
public class VaultConfig implements EnvironmentPostProcessor {
    
    @Override
    public void postProcessEnvironment(ConfigurableEnvironment env, SpringApplication app) {
        env.getPropertySources().addFirst(new VaultPropertySource(client));
    }
}

Question 28: How to refresh configuration on the fly?

Answer:

@RefreshScope
@Component
public class DynamicConfig {
    
    @Value("${app.feature.enabled}")
    private boolean enabled;
}

# With Spring Cloud Config
curl -X POST http://localhost:8080/actuator/refresh

@RefreshScope beans are recreated.

Question 29: How to test configuration properties?

Answer:

@SpringBootTest(properties = {
    "app.name=Test App",
    "app.timeout=1000"
})
class ConfigTest {
    
    @Autowired
    private AppProperties properties;
    
    @Test
    void propertiesLoaded() {
        assertThat(properties.getName()).isEqualTo("Test App");
        assertThat(properties.getTimeout()).isEqualTo(1000);
    }
}

// Or with test file
@SpringBootTest
@TestPropertySource("classpath:test-config.properties")
class ConfigTest { }

Question 30: What are the best practices for configuration?

Answer:

Type with @ConfigurationProperties
Validate with @Validated
Externalize secrets
Document each property
Sensible default values
Profiles for environments
Do not commit secrets
Centralize with Config Server in microservices

@ConfigurationProperties(prefix = "app")
@Validated
public class AppProperties {
    
    /**
     * Application name displayed in logs.
     */
    @NotBlank
    private String name = "My Application";
}

Score

Score	Level
27-30	Excellent - Mastered scopes and configuration
21-26	Good - Some revisions needed
15-20	Average - Review the chapter
Less than 15	Needs improvement

Back to Module 5

Questions 1-15: Scopes​

Questions 16-30: Configuration​

Score​

Questions 1-15: Scopes

Questions 16-30: Configuration

Score