Planned lessonJNR-009-L04

Multiple implementations

Lesson 4 of 8
Junior

On This Lesson 4 topics

In this lesson
Planned topics
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Practice

This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.

In this lesson

resolve ambiguity with @Primary and @Qualifier.

Planned topics

Two beans of the same type make Spring unable to choose: NoUniqueBeanDefinitionException.
@Primary marks the default choice.
@Qualifier("name") at the injection point picks a specific bean.
Injecting a List<PricingStrategy> collects all implementations.
Bean names default to the class name with a lowercase first letter.

Draft outline details

Demonstration

java

@Component @Primary class StripePayment implements PaymentProvider {}
@Component("paypal") class PayPalPayment implements PaymentProvider {}

OrderService(@Qualifier("paypal") PaymentProvider payment) { ... }

Check your understanding

You want one default and one exception. Which annotations?

Show answer

@Primary on the default, @Qualifier where the exception is used.

Practice

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