How do you add custom method impls to all repositories & specific ones?

[matthewadams]

Consider the following custom repository interface:

@NoRepositoryBean
public interface CustomRepository<T, ID extends Serializable>
    extends JpaRepository<T,ID> {

    void doSomethingInteresting(); // common to all repositories
}

Its implementation:

public class SimpleJpaCustomRepository<T, ID extends Serializable>
    extends SimpleJpaRepository<T,ID> {

    public void doSomethingInteresting() { /* ... */ }
}

Another custom repository interface:

public interface FooRepository
    extends CustomRepository<Foo,Long> {

    List<Foo> findByBarLike(String criteria); // SD JPA dynamic finder

    List<Foo> findByBarStartingWith(String criteria); // my own finder
}

Now, if the implementation of findByBarStartingWith is

public List<Foo> findByBarStartingWith(String criteria) {

    String intendedCriteria = criteria.replace("_", "\\_").replace("%", "\\%") + "%";

    return findByBarLike(intendedCriteria); // from SD JPA via "this"?
}

in what class do I put this method yet still have SD JPA provide an implementation of findByBarLike? Would it be available via this or some other reference? How would I configure this in my Spring context?