为什么@Autowired 不适用于泛型类型 T？

Question

I have below class where I am trying to inject some JpaRepository dependency.

class Sample<T> implements SampleInterface<T> {
  @Autowired
  JpaRepository<T, Long> jpaRepository; // Want this to be injected by spring using A as entity
}


 class Main {
    @Bean
    Sample<A> sample() {
      return new Sample<A>(); // A is a jpa entity
    }
 }

Is it because annotations are parsed during compilation? Why can't spring make the autowiring dynamic using generics? I may be missing the fundamentals, but curious to fill that knowledge gap.

Answer 1

The reason for this is type erasure which happens at compile time while bean injection happens at runtime.

Since there are no bounds on it T gets erased and basically replaced by Object and Spring Data can't create repositories for Object .

See also Using generics in Spring Data JPA repositories