Setter-based/method-based injection

The second way is to declare a method, usually a setter, and apply the @Autowired annotation or the @Required annotation to it. For example, we can remove the MessageService constructor and add a setRepository(MessageRepository) method, as follows:

public class MessageService {
   ...
   @Required
   public void setRepository(MessageRepository repository) {
     this.repository = repository;
   }
   ...
}

Or, you can name it something else, such as the following:

@Autowired
public void prepare (MessageRepository repository) {
  this.repository = repository;
}