How to correctly implement a strategy pattern with Spring Boot and handle bean lifecycle events?
I'm trying to implement the strategy design pattern in my Spring Boot application to handle different payment methods. I have created an interface `PaymentStrategy` and several implementations like `CreditCardPayment` and `PayPalPayment`. However, I'm facing issues with the bean lifecycle where the context doesn't inject the right strategy implementation based on user selection. I've annotated my strategy classes with `@Component`, but they aren't being picked up correctly when I try to use them in my service class. Here’s a simplified version of my `PaymentStrategy` interface and implementations: ```java public interface PaymentStrategy { void pay(int amount); } @Component public class CreditCardPayment implements PaymentStrategy { @Override public void pay(int amount) { System.out.println("Paid " + amount + " using Credit Card."); } } @Component public class PayPalPayment implements PaymentStrategy { @Override public void pay(int amount) { System.out.println("Paid " + amount + " using PayPal."); } } ``` In my service class, I have a method that is supposed to select the appropriate payment strategy: ```java @Service public class PaymentService { private final Map<String, PaymentStrategy> strategies; @Autowired public PaymentService(List<PaymentStrategy> strategies) { this.strategies = strategies.stream().collect(Collectors.toMap(Object::getClass, Function.identity())); } public void processPayment(String type, int amount) { PaymentStrategy strategy = strategies.get(type); if (strategy == null) { throw new IllegalArgumentException("No such payment method: " + type); } strategy.pay(amount); } } ``` When I call `processPayment("CreditCardPayment", 500)`, I keep getting an `IllegalArgumentException` even though I have registered `CreditCardPayment` and `PayPalPayment` as beans. The message indicates that the strategy is null. I suspect there’s an issue with how I'm trying to collect the strategies into a map, but I'm not sure how to properly manage the lifecycle and selection of these beans. I've also tried using `@Qualifier` on the constructor parameters, but that didn’t help. Any insights on what I might be doing wrong or how to better achieve this using Spring Boot? I'm using Spring Boot version 2.5.4.