Autowiring a Generic Implementation. Error: NoSuchBeanDefinitionException-CodePudding

Below are the classes and the error mentioned. Spring version: 5

public interface CustomGenerator<T,R> {
  void generate();
}

@Service
public abstract class AbstractGenerator<T extends CustomClassA, R extends CustomClassB>
implements CustomGenerator<T,R> {}

@Service
public class ConcreteC1 extends AbstractGenerator<CustomClassA, CustomClassB>{

 void generate(){
  ...
 }
}

@Service
public class ConcreteC2 extends AbstractGenerator<CustomClassA, CustomClassB>{

 void generate(){
  ...
 }
}

@Service
public class CustomService {

@Autowired
private List<CustomGenerator<CustomClassA, CustomClassB>> customGenerators;
// Expected: ConcreteC1 & ConcreteC1 instances in the list

}

Error: org.springframework.beans.factory.UnsatisfiedDependencyException Unsatisfied dependency expressed through field 'customGenerators' nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type.

I want a list of concrete classes instead of utilizing qualifiers to pick one by one, as I want to execute the generate method for all the elements in the list at once. Thanks for any help in advance.

CodePudding user response：

Generic programming in java is not easy.
We can try to solve this by adding a base class for generic type.

class ConcreteBase extends AbstractGenerator<CustomClassA, CustomClassB> {
    ...
}

And rewrite our ConcreteX class:

class ConcreteX extends ConcreteBase {
    ...
}

After that, rewrite the type of List:

@Service
public class CustomService {
    @Autowired
    private List<ConcreteBase> customGenerators;
}

Spring will help to inject the list with ConcreteX bean.

CodePudding user response：

Tested this example as exactly as I could with version 5.3.2 and it seems to work for me.

Perhaps your problem is something different? Some follow up questions that might help getting to the bottom of it:

Are all the classes correctly configured in the component scan, for example?
Exact spring version info

CodePudding user response：

The below fix while autowiring made this silly mistake go away. Thanks, everyone for your time & responses :)

@Service
public class CustomService {

@Autowired
private List<CustomGenerator<? extends CustomClassA, ? extends CustomClassB>> customGenerators;

}