春天不创造豆

Question

I have two beans that implements the same interface. Both are created in Java configuration, like this:

@Bean
@Qualifier("kafkaEventSender")
public IKafkaEventSender<KafkaData> kafkaEventSender(@Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
    return new KafkaEventSender<>(kafkaTemplate, false);
}

@Bean
@Qualifier("kafkaEventSenderAudited")
public IKafkaEventSender<KafkaData> kafkaEventSenderAudited(@Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
    return new KafkaEventSenderAudited<>(kafkaTemplate, false);
}

The problem is that spring doesn't create first bean only the second. Any idea why?

Answer 1

Try using bean names instead:

@Bean(name = "kafkaEventSender")
public IKafkaEventSender<KafkaData> kafkaEventSender(@Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
    return new KafkaEventSender<>(kafkaTemplate, false);
}

@Bean(name = "kafkaEventSenderAudited")
public IKafkaEventSender<KafkaData> kafkaEventSenderAudited(@Qualifier("EventBus") KafkaTemplate<String, Object> kafkaTemplate){
    return new KafkaEventSenderAudited<>(kafkaTemplate, false);
}

Answer 2

Ok, the problem was with method name, after changing it, bean is properly created. In some other library configuration class was a method with same name. Guessing that was the problem.

Answer 3

@Qualifier annotation is used to select one bean over multiple available beans of same type in spring container.

when you annotate a method with @Bean annotation, default, it creates a bean whose name is the name of same method. So, for example:

    @Bean
    public BeanA itsBeanA() {
        return new BeanA();
    }

    @Bean(name = "specialBeanA")
    public BeanA itsAgainBeanA() {
        return new BeanA("specialConstructorParam");
    }

    @Bean
    public BeanB beanB(@Autowired @Qualifier("specialBeanA") BeanA beanA) {
        return new BeanB(beanA);
    }

first method will create an instance of BeanA with name 'itsBeanA'. Second, will create an instance with name 'specialBeanA' since we provided the name attribute here. There maybe a scenario where you need to have multiple beans of same TYPE (like BeanA here). It will create ambiguity for container which bean to use of all same types, we specify the @Qualifier with the name of bean which we want. I hope that helps.