Important Annotations Interview Questions

@SpringBootApplication combines @SpringBootConfiguration, @EnableAutoConfiguration, and @ComponentScan. Together they mark the main configuration class, enable conditional setup, and scan the application package.

@EnableAutoConfiguration tells Spring Boot to consider its auto-configuration classes. @SpringBootApplication already includes this annotation, so it is rarely written separately.

All four are component stereotypes detected during scanning. @Component is general, @Service represents business logic, @Repository represents persistence and translates database exceptions, and @Controller handles web requests.

@RestController combines @Controller and @ResponseBody, so handler results are written directly as JSON or another response body. A normal @Controller usually returns a view name unless a method uses @ResponseBody.

@Component is placed on a class discovered by component scanning. @Bean is placed on a method inside configuration and is useful when creating a third-party class or when construction needs custom code.

@Configuration marks a class as a source of bean definitions. Methods annotated with @Bean are registered in the ApplicationContext and can receive injected dependencies.

@Value injects one property or expression into a field, constructor parameter, or method parameter. It is convenient for a small number of values, but grouped settings are usually clearer with @ConfigurationProperties.

@Configuration marks a class as a source of bean definitions. Methods annotated with @Bean are registered in the ApplicationContext and can receive injected dependencies.

@Value is concise for individual values. @ConfigurationProperties is better for a related group of settings because it provides a typed object, clear prefixes, and validation.

@Profile limits a bean or configuration class to selected environments such as dev, test, or prod. The active profile decides which definitions are loaded.