What are the different ways to configure Spring applications?

Spring supports three ways to configure an application: XML files, annotations on your classes, and Java configuration classes.

1. XML-based configuration declares beans and their wiring in XML files. It appears mostly in older projects.
2. Annotation-based configuration marks classes with @Component and injection points with @Autowired, and component scanning finds them.
3. Java-based configuration uses @Configuration classes whose @Bean methods create beans.

// Java-based configuration
@Configuration
public class AppConfig {
    @Bean
    public UserService userService() {
        return new UserService(userRepository());
    }
    
    @Bean
    public UserRepository userRepository() {
        return new UserRepository();
    }
}

Most applications mix the last two. Annotations cover your own classes, and @Bean methods cover third-party classes you cannot annotate. Spring Boot can still load an old XML file with @ImportResource.