Spring@AutowiredforListTypes

Z时代
2024-01-10
分类：综合

Let’s see an example - we have three pets that we’d like to register them on the public animal registry.

publicabstractclassAnimal{ ... }

@Component
publicclassMyDogextendsAnimal{ ... }

@Component
publicclassMyCatextendsAnimal{ ... }

@Component
publicclassMyBirdextendsAnimal{ ... }

The question is - how to register all my animals?

@Component
publicclassAnimalRegistry{
private Map<String, Animal> registry;
// How to register all my animals to the registry?
}

Naive Approach

@Component
publicclassAnimalRegistry{
private Registry<Animal> registry;
/**
    * This is naive because if you have more animals,
    * you have to specify them explicitly here
    */
@Autowired
publicAnimalRegistry(MyDog dog, MyCat cat, MyBird bird){
        registry.register(dog);
        registry.register(cat);
        registry.register(bird);
    }
}

Have Spring Autowire All Subclass

@Component
publicclassAnimalRegistry{
private Registry<Animal> registry;
/**
		* The problem with this approach is that
		* if you don"t have any animals, there"s no bean to be autowired here, 
		* and Spring will report bean initialization error
		*/
@Autowired
publicAnimalRegistry(List<Animal> myAnimals){
if(myAnimals != null && !myAnimals.isEmpty()) {
            myAnimals.forEach(a -> registry.register(a));
        }
    }
}

Better Usage of `@Autowired`

@Component
publicclassAnimalRegistry{
private Registry<Animal> registry;
@Autowired(required = false)
    List<Animal> myAnimals;
/**
		* This ensures that Spring can still successfully run
		* even when there"s no bean to be autowired to "myAnimals" 
		*/
@PostConstruct
publicvoidinit(){
if(myAnimals != null && !myAnimals.isEmpty()) {
            myAnimals.forEach(a -> registry.register(a));
        }
    }
}

This tip should work well w.r.t interfaces

public inteface Provider { ... }

@Component
publicclassDogProviderimplementsProvider{ ... }

@Component
publicclassCatProviderimplementsProvider{ ... }

@Component
publicclassBirdProviderimplementsProvider{ ... }

@Component
publicclassProviderRegistry{
private Registry<Provider> registry;
@Autowired(required = false)
    List<Provider> providers;
@PostConstruct
publicvoidinit(){
if(providers != null && !providers.isEmpty()) {
            providers.forEach(a -> registry.register(a));
        }
    }
}