@Autowired
This annotation is applied to fields, setter methods, and constructors. The @Autowired annotation injects object dependency implicitly.
@Configuration
This annotation is used on classes that define beans.
@Configuration is an analog for an XML configuration file, it is configuration using Java classes.
A Java class annotated with @Configuration is a configuration by itself and will have methods to instantiate and configure the dependencies.
Annotated classes will be processed by the Spring container to generate bean definitions and service requests for those beans at runtime.
@Configuration is also a @Component. This means subject to component-scanning
But: @Configuration classes may not only be bootstrapped using component scanning, but may also themselves configure component scanning using the @ComponentScan annotation
One @Configuration may be injected into another using @Import(OtherConfig) via constructor injection.
@Bean
This annotation is used at the method level.
The @Bean annotation works with @Configuration to create Spring beans.
As mentioned earlier, @Configuration will have methods to instantiate and configure dependencies.
Such methods will be annotated with @Bean.
The method annotated with this annotation works as the bean ID, and it creates and returns the actual bean.
@Lazy
This annotation is used on component classes.
By default, all autowired dependencies are created and configured at startup.
But if you want to initialize a bean lazily, you can use the @Lazy annotation over the class.
This means that the bean will be created and initialized only when it is first requested for.
You can also use this annotation on @Configuration classes.
This indicates that all @Bean methods within that @Configuration class should be lazily initialized.
@Component
This annotation is used on classes to indicate a Spring component.
The @Component annotation marks the Java class as a bean or component so that the component-scanning mechanism of Spring can add it into the application context.
@Controller
The @Controller annotation is used to indicate the class is a Spring controller.
This annotation can be used to identify controllers for Spring MVC or Spring WebFlux.
@Service
This annotation is used on a class.
@Service marks a Java class that performs some service, such as executing business logic, performing calculations, and calling external APIs.
This annotation is a specialized form of the @Component annotation intended to be used in the service layer.
@Repository
This annotation is used on Java classes that directly access the database.
The @Repository annotation works as a marker for any class that fulfills the role of repository or Data Access Object.
This annotation has an automatic translation feature.
For example, when an exception occurs in the @Repository, there is a handler for that exception and there is no need to add a try-catch block.