Spring Boot Core Annotations

✅ 4) Spring Boot Annotations (Core)

🔹 Definition:

Spring Boot provides a set of annotations to simplify configuration, auto-wiring, and REST API creation.

Annotation	What It Does	Where Used
@SpringBootApplication	Combines @Configuration, @EnableAutoConfiguration, @ComponentScan	Main class
@ComponentScan	Scans packages for beans/components	Main class or config class
@EnableAutoConfiguration	Enables automatic configuration based on dependencies	Main class
@RestController	Combines @Controller and @ResponseBody	REST controller
@RequestMapping	Maps HTTP requests	On methods or classes
@Autowired	Injects dependencies	Fields, constructors
@Value	Injects properties from application.properties	Fields
@Bean	Registers a method’s return as a Spring bean	Inside @Configuration
@Configuration	Declares a configuration class	Any config class

1. @SpringBootApplication




Marks the main class of a Spring Boot application.
It combines @Configuration, @EnableAutoConfiguration, and @ComponentScan.
This annotation triggers auto-configuration, component scanning, and Java-based configuration.
It is typically placed on the entry-point class containing the main() method.

2. @Configuration

Indicates that the class declares one or more Spring beans.

Used to define beans using Java configuration instead of XML.

Each method annotated with @Bean inside this class returns an object to be managed by Spring.

Commonly used for custom configuration classes.

3. @ComponentScan

Tells Spring where to look for annotated components (like @Component, @Service, etc.).
By default, it scans the package where the main class is located and its subpackages.
Used when you want to explicitly define the base packages to scan.
It helps Spring find and register beans automatically.

4. @EnableAutoConfiguration

Enables Spring Boot’s auto-configuration feature.

Based on classpath dependencies, it auto-configures beans and settings.
Part of @SpringBootApplication, but can be used separately.
Saves effort in manual configuration of common components like DataSource, MVC, etc.

5. @Bean

Declares a bean manually inside a @Configuration class.
Returned object is managed by the Spring container.
Useful for third-party libraries or custom instantiations.
Provides full control over bean instantiation.
@Bean
public MyService myService() {
    return new MyServiceImpl();
}

✅ Spring Boot Feature Enabling Annotations

Annotation	Purpose
@EnableCaching	Enables caching mechanism
@EnableScheduling	Enables scheduled tasks via @Scheduled
@EnableAsync	Enables asynchronous execution with @Async
@EnableJpaRepositories	Enables Spring Data JPA repositories
@EnableTransactionManagement	Enables transaction support