Multiple beans implement the same interface. What are your tools to control which gets injected?

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The strategy-registry idiom

interface PaymentProvider { String key(); Receipt charge(Order o); }

@Component class StripeProvider implements PaymentProvider { … }
@Component class AdyenProvider  implements PaymentProvider { … }

@Service
class PaymentRouter {
    private final Map<String, PaymentProvider> byKey;
    PaymentRouter(List<PaymentProvider> providers) {      // ALL impls injected
        this.byKey = providers.stream()
            .collect(toMap(PaymentProvider::key, p -> p));
    }
    Receipt charge(String provider, Order o) {
        return byKey.get(provider).charge(o);             // open/closed: new provider
    }                                                      // = new @Component, zero edits
}

// Type-safe qualifier beats string matching:
@Qualifier @Retention(RUNTIME) @interface Sandbox {}
@Component @Sandbox class SandboxProvider implements PaymentProvider { … }
PaymentRouter(@Sandbox PaymentProvider p) { … }

Map<String, T> injection keys by bean name — handy, but a custom key() method survives renames better.
@Primary = 'the default'; @Qualifier = 'this specific one'; combining them models default-plus-overrides cleanly (e.g., primary real client, qualified test double).
ObjectProvider<T> handles optional deps (getIfAvailable), lazy resolution, and streams of candidates without container exceptions.
Profiles/@ConditionalOn… remove ambiguity at registration time rather than injection time — often the cleanest cut.

Multiple beans implement the same interface. What are your tools to control which gets injected?

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