Injecting Collection of Interface Type into Method Annotated with @Bean

Question

Using Spring and given several classes that implement a common interface, how would I reference all classes that implemented this interface using the @Bean annotation at the method level?

I want to retrieve all implementing instances, apply some logic to each instance, then return a managed Map<String, Animal> object which can be injected to other classes or components.

Common Interface(s)

public interface Animal {

   String makeNoise();

}

public interface Person {

   String getOccupation();

}

Animal Implementation #1

public Dog implements Animal {

   @Override
   String makeNoise() {
      return "Bark! Bark!";
   }

} 

Animal Implementation #2

public Cat implements Animal {

   @Override
   String makeNoise() {
      return "Meow! Meow!";
   }

} 

Person Implementation #1

public Developer implements Person {

   @Override
   public String getOccupation() {
      return "Software Engineer";
   }

}

Person Implementation #2

public Lawyer implements Person {

   @Override
   public String getOccupation() {
      return "Litigator";
   }

}

Configuration

@Configuration
public class Initialize {

   //<snip> Beans created for Developer, and Lawyer objects </snip>

   @Bean
   Map<String, Developer> getDevelopers(List<Developer> developers) { // This is fine
      return new HashMap<>(...);
   }

   @Bean
   Map<String, Lawyer> getLawyers(List<Person> people) { // Spring wires this dependency fine
      return new HashMap<>(...);
   }

   @Bean
   Map<String, Dog> getOwners(Map<String, Person> owners) { // Spring reports it cannot auto-wire this dependency
                                                            // what do I do here? 
   }

}

Any help would be appreciated, thanks!

Answer 1

Try this kind of configuration. The only point here is that the order of beans in the collection is random and can't be under control.

    @Configuration
    public class CollectionConfig {

        @Bean
        public Animal getCat() {
            return new Cat();
        }

        @Bean
        public Animal getDog() {
            return new Dog();
        }

        @Bean
        Map<String, Animals> gatherAnimals(List<Animals> animals) {
           // any code
        }
    }

Here is more about that https://www.baeldung.com/spring-injecting-collections

Answer 2

Need to leverage co-variance with a List . See below pseudo-code/code snippet.

@Configuration
public class Initialize {

   //<snip> Beans created for Developer, and Lawyer objects </snip>

   @Bean
   Map<String, Developer> getDevelopers(List<Developer> developers) {
      return new HashMap<>(...);
   }

   @Bean
   Map<String, Lawyer> getLawyers(List<Person> people) {
      return new HashMap<>(...);
   }

   @Bean
   Map<String, Dog> getOwners(List<Map<String, ? extends Person>> owners) { // Spring will auto-wire the "owners" variable 
                                                                            // with all bean objects that match this signature 
                                                                            // (✅ Map<String, Lawyer>, ✅ Map<String, Developer> ...)

   }

}

Resources:

• Spring: get all Beans of certain interface AND type