1. CREATIONAL Patterns

Common Patterns

Pattern	Purpose	Spring Boot Example
Singleton	One instance per context	@Bean, @Component (default scope is singleton)
Factory Method	Subclass decides which class to instantiate	Custom ServiceFactory that returns different PaymentService
Abstract Factory	Create families of related objects	Return groups of beans depending on profile/environment
Builder	Step-by-step object construction	UriComponentsBuilder, ResponseEntityBuilder
Prototype	New instance every time	Spring's @Scope("prototype")

2. STRUCTURAL Patterns

🔹 What they solve: Object composition—how objects fit together to form larger structures. 🔹 Goal: Help classes work together while keeping them flexible and decoupled.

Common Patterns

Pattern	Purpose	Spring Boot Example
Adapter	Makes incompatible interfaces work together	JdbcTemplate as an adapter over JDBC; Spring Security’s UserDetailsAdapter
Facade	Simplifies complex APIs	RestTemplate, WebClient, or service layer wrapping complex logic
Proxy	Adds behavior without changing original object	Spring AOP Proxies (logging, security)
Decorator	Adds behavior dynamically	HandlerInterceptor, Filter, Spring Web Decorators
Bridge	Decouples abstraction from implementation	Spring Data JPA (CrudRepository) bridges to underlying DB logic

3. BEHAVIORAL Patterns

🔹 What they solve: Object communication and responsibility sharing 🔹 Goal: Define how objects interact and pass responsibilities between them.

🔧 Common Patterns

Pattern	Purpose	Spring Boot Example
Strategy	Select algorithm at runtime	AuthenticationProvider, conditional @Bean injection
Observer	Notify objects when state changes	@EventListener, ApplicationEventPublisher
Template Method	Define algorithm structure, let subclasses customize	Spring’s JdbcTemplate, RestTemplate, AbstractController
Command	Encapsulate a request as an object	Spring Batch Jobs, Runnable commands
Chain of Responsibility	Pass requests along a chain of handlers	Spring Security Filter Chain, Servlet Filter Chain