Spring. How bean injection works when there are more than one bean with the same qualifier?

Question

Lets assume you have the following Classes extending the Processor interface:

Interface Processor {}

class ProcesorImpl1 implements Processor {}

class ProcesorImpl2 implements Processor {}

Now, Lets assume that you define the following bean in a configuration class in package1:

class ConfigurationClass1 {

    @Bean
    @Qualifier("processor")
    public Processor processor() {
         return new ProcesorImpl1();
    }

}

Next, you define the following bean in a configuration class in package2:

class ConfigurationClass2 {

    @Bean
    @Qualifier("processor")
    public Processor anotherProcessor() {
         return new ProcesorImpl2();
    }

}

The question is how does Spring resolves the following Injection:

@Inject @Qualifier("processor") proc;

What if one of the Beans are annotated with @Primary?

Artur Vakhrameev Artur Vakhrameev · Accepted Answer · 2019-01-18T12:26:49

Qualifier doesn't work with @Bean annotation, but @Primary does and it will define what concrete bean will be injected if you inject a bean by type and there is multiple bean of this type managed by Spring. If you want to inject another non-primary bean, you can mark it with @Qualifier("beanName") annotation to inject it by name. If you define 2 bean with the same names and the same types like this

class ConfigurationClass1 {

    @Bean("processor")
    public Processor processor() {
         return new ProcesorImpl1();
    }

}

class ConfigurationClass2 {

    @Bean("processor")
    public Processor anotherProcessor() {
         return new ProcesorImpl2();
    }

}

Spring will override the first loaded bean within the second and only single will stay in container, because of allowBeanDefinitionOverriding property is set to true by default.

Spring. How bean injection works when there are more than one bean with the same qualifier?

1 Answers