spring Creating and using beans Autowiring all beans of a specific type
Example
If you've got multiple implementations of the same interface, Spring can autowire them all into a collection object. I'm going to use an example using a Validator pattern1
Foo Class:
public class Foo {
private String name;
private String emailAddress;
private String errorMessage;
/** Getters & Setters omitted **/
}
Interface:
public interface FooValidator {
public Foo validate(Foo foo);
}
Name Validator Class:
@Component(value="FooNameValidator")
public class FooNameValidator implements FooValidator {
@Override
public Foo validate(Foo foo) {
//Validation logic goes here.
}
}
Email Validator Class:
@Component(value="FooEmailValidator")
public class FooEmailValidator implements FooValidator {
@Override
public Foo validate(Foo foo) {
//Different validation logic goes here.
}
}
You can now autowire these validators individually or together into a class.
Interface:
public interface FooService {
public void handleFoo(Foo foo);
}
Class:
@Service
public class FooServiceImpl implements FooService {
/** Autowire all classes implementing FooValidator interface**/
@Autowired
private List<FooValidator> allValidators;
@Override
public void handleFoo(Foo foo) {
/**You can use all instances from the list**/
for(FooValidator validator : allValidators) {
foo = validator.validate(foo);
}
}
}
It's worth noting that if you have more than one implementation of an interface in the Spring IoC container and don't specify which one you want to use with the @Qualifier annotation, Spring will throw an exception when trying to start, because it won't know which instance to use.
1: This is not the right way to do such simple validations. This is a simple example about autowiring. If you want an idea of a much easier validation method look up how Spring does validation with annotations.
