Use @Qualifier to inject collections groups in Spring

When using collection dependency injection in Spring, sometimes it's necessary to group multiple beans of the same type. This can be achieved by using either @Qualifier or custom qualifier annotations.

@Qualifier

@Configuration
public class QualifiedBeansConfig {
    private static final Logger log = LoggerFactory.getLogger(QualifiedBeansConfig.class);

    public static final String MY_QUALIFIER_A = "MY_QUALIFIER_A";
    public static final String MY_QUALIFIER_B = "MY_QUALIFIER_B";

    @Bean
    @Qualifier(MY_QUALIFIER_A)
    public MyBean myBean1() {
        return new MyBean("1");
    }

    @Bean
    @Qualifier(MY_QUALIFIER_A)
    public MyBean myBean2() {
        return new MyBean("2");
    }

    @Bean
    @Qualifier(MY_QUALIFIER_B)
    public MyBean myBean3() {
        return new MyBean("3");
    }

    @Component
    public static class BeanCollections {
        public BeanCollections(final List<MyBean> myBeansList,
                        @Qualifier(MY_QUALIFIER_A) final Set<MyBean> myBeansSet,
                        @Qualifier(MY_QUALIFIER_B) final Map<String, MyBean> myBeansMap
        ) {
            log.info("myBeansList: {}", myBeansList);
            log.info("myBeansSet: {}", myBeansSet);
            log.info("myBeansMap: {}", myBeansMap);
        }
    }
}

Output

...   : myBeansList: [MyBean[key=1], MyBean[key=2], MyBean[key=3]]
...   : myBeansSet: [MyBean[key=1], MyBean[key=2]]
...   : myBeansMap: {myBean3=MyBean[key=3]}

Custom Qualifier Annotation

Another approach is to use Custom Qualifier Annotation：

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface QualifierA {
}

@Target({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER, ElementType.TYPE, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Qualifier
public @interface QualifierB {
}

Replace

• @Qualifier(MY_QUALIFIER_A) to @QualifierA
• @Qualifier(MY_QUALIFIER_B) to @QualifierB

to achieve the same goal.