@Configuration Annotation in Spring Boot

@Configuration is a Spring annotation that indicates that a class declares one or more @Bean methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime, for example:

@Configuration
public class AppConfig {

  @Bean
  public MyService myService() {
    return new MyServiceImpl();
  }
}

Here, the @Configuration annotation indicates that the AppConfig class contains one or more bean methods and the @Bean annotation on the myService method indicates that this method returns an object that should be registered as a bean in the Spring application context.

To use the @Configuration annotation, you will need to have the Spring Framework on your classpath. If you are using Spring Boot, the Spring Framework is already included as a dependency, so you can use the @Configuration annotation without any additional configuration.

To use the @Configuration annotation in a Spring Boot application, you can follow these steps:

1. Create a new Java class and annotate it with @Configuration.
2. Add @Bean methods to the class to define beans for the application context.
3. In your main application class, annotate it with @EnableAutoConfiguration or @SpringBootApplication to enable Spring Boot’s auto-configuration features.

For example, consider the following AppConfig class:

@Configuration
public class AppConfig {

  @Bean
  public MyService myService() {
    return new MyServiceImpl();
  }
}

To use this configuration class in a Spring Boot application, you can create a main application class with the @EnableAutoConfiguration or @SpringBootApplication annotation, like this:

@EnableAutoConfiguration
@Import(AppConfig.class)
public class MyApplication {

  public static void main(String[] args) {
    SpringApplication.run(MyApplication.class, args);
  }
}

Alternatively, you can use the @SpringBootApplication annotation, which combines @Configuration, @EnableAutoConfiguration, and @ComponentScan:

@SpringBootApplication
public class MyApplication {

  public static void main(String[] args) {
    SpringApplication.run(MyApplication.class, args);
  }
}

With either of these approaches, Spring Boot will scan for @Configuration classes and use them to configure the application context. The @Bean methods in these classes will be used to create and register beans with the application context.

You can also use the @Configuration annotation in combination with @ComponentScan to enable component scanning for your application. For example:

@Configuration
@ComponentScan("com.example.myapp")
public class AppConfig {
  ...
}

This will cause Spring to scan the specified package, and its subpackages for classes annotated with @Component or other Spring-specific annotations and register them as beans in the application context.

I hope this helps!

To learn more, check out the Spring Boot tutorials page.