Spring Boot Auto-Configuration and Starters Questions and Answers

Question 1

What is the primary mechanism Spring Boot uses to trigger auto-configuration based on the contents of the classpath?

Accepted Answer

The presence of specific 'starter' dependencies in the build configuration.

Answer

Scanning for classes annotated with @Component in third-party JARs.

Answer

Explicitly importing configuration classes using @Import in the main application class.

Answer

Reading bean definitions from XML files found in the META-INF directory.

Question 2

A developer wants to prevent `DataSourceAutoConfiguration` from running because they intend to define a custom `DataSource` bean. Which of the following is a valid way to achieve this?

Accepted Answer

Set the property `spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration` in `application.properties`.

Answer

Add `@ComponentScan(excludeFilters = @Filter(type = FilterType.ASSIGNABLE_TYPE, classes = DataSourceAutoConfiguration.class))` to the main application class.

Answer

Create a bean named `excludeDataSourceAutoConfiguration` in any `@Configuration` class.

Answer

Comment out the `@EnableAutoConfiguration` annotation.

Question 3

In a custom Spring Boot starter, which file is the modern standard (since Spring Boot 2.7) for registering auto-configuration classes so that they can be discovered by other applications?

Accepted Answer

META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports

Answer

META-INF/spring.factories

Answer

META-INF/services/org.springframework.boot.autoconfigure.EnableAutoConfiguration

Answer

resources/autoconfiguration.properties

Question 4

A Spring Boot application needs to configure a `NotificationService` bean, but only if a property `notification.service.enabled` is set to `true` in the `application.properties`. Which annotation should be used on the bean definition?

Accepted Answer

@ConditionalOnProperty(name = "notification.service.enabled", havingValue = "true")

Answer

@ConditionalOnClass(name = "notification.service.enabled")

Answer

@ConditionalOnBean(name = "notification.service.enabled")

Answer

@ConditionalOnExpression("'${notification.service.enabled}' == 'true'")

Question 5

A developer includes the `spring-boot-starter-data-jpa` dependency. They do not define a `DataSource` bean but provide the necessary database connection details in `application.properties`. What is the expected outcome?

Accepted Answer

Spring Boot will auto-configure a `DataSource`, a `JpaTransactionManager`, and an `EntityManagerFactory`.

Answer

The application will fail to start because a `DataSource` bean must always be explicitly defined.

Answer

The application will start, but database operations will fail at runtime due to a missing `EntityManagerFactory`.

Answer

Spring Boot will not configure anything related to the database, requiring manual setup.

Question 6

Which of the following best describes the relationship between Spring Boot Starters and Auto-Configuration?

Accepted Answer

Starters provide dependencies, and auto-configuration uses the presence of those dependencies on the classpath to configure beans.

Answer

Starters are a replacement for auto-configuration in modern Spring Boot versions.

Answer

Auto-configuration is a feature used to create custom starter dependencies.

Answer

Auto-configuration must be manually triggered by a property within the starter's `pom.xml`.