In Spring, both the Singleton and Factory patterns play essential roles in managing objects (beans) and ensuring flexibility, simplicity, and maintainability in your application.

Singleton Pattern:

Spring uses the Singleton pattern by default for all beans. When a bean is defined, Spring creates only one instance per container, and this instance is reused throughout the application. This helps with consistency and efficient resource management.

Example: In your code, the @Service annotated MyService is a singleton. This means there will only be one instance of MyService, which is injected into the controller and reused across requests.

Factory Pattern:

Spring also applies the Factory pattern through configuration classes and factory methods. Instead of directly instantiating objects, you define beans in configuration classes (such as AppConfig), where the actual creation of objects can be controlled and altered as needed.

Example: In your example, the @Bean method in the AppConfig class demonstrates the Factory pattern by providing a flexible way to create instances of MyServiceImpl. This decouples the instantiation logic from the actual use of the service, promoting loose coupling.

By using these patterns, Spring simplifies the process of dependency management and ensures that your application remains scalable and maintainable.