Enhancement: @UniqueBean on interface or unique-beans: Class[] in application.yml

We like having interfaces define a contract for beans, and we also like having things like auto-configuration.

However, we can have situations where we know we only want there to ever be one implementation of an interface in the bean registry.

As a developer or perhaps even ops, I want to have duplicate bean definitions caught early instead of at the @Autowired site.

Would it work to either have something like:

package com.acme;

@UniqueBean
interface MyBean {
}

or

application.yml

spring:
  unique-beans:
    - com.acme.MyBean

We could then get a different exception thrown for this scenario, and and a far simpler exception report than the NoUniqueBeanDefinitionException report which is often not the information that is best to diagnose the cause of the duplication.

Start by reviewing Spring's bean registry and the existing @Autowired handling around NoUniqueBeanDefinitionException. Compare the proposed @UniqueBean interface annotation with the application.yml unique-beans configuration, then define the exception behavior and configuration scope before identifying implementation and test locations.