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Re: [ljc] RFC - Default service implementation structure

From: Gerald L.
Sent on: Thursday, March 7, 2013 8:06 AM
I assume that any technology that depends on class-path scanning to
automatically discover your service implementation (without you having
to register it anywhere) will only find it if it is a top-level class.
This means that your nested default service implementations cannot
- be annotated with @Stateless to become stateless session beans
- be CDI managed beans (which doesn't require them to be annotated)
and so cannot be @Inject-ed
- be annotated with Spring's @Component (or similar) in order to be
auto-discovered as Spring beans
- be auto-discovered as SOAP or REST webservice implementations
- and probably many more.

This is a purely technical point, of course.


On Mon, Mar 4, 2013 at 12:25 PM, Wesley Hall <[address removed]> wrote:
> Hello folks,
> I have a little issue that I am sure has crossed the minds of a few
> folks here and thought I would open it up for comments.
> I am currently working on one of my little toy projects. I usually
> have at least one of these on the go at any given point as it allows
> me to play with new versions of libraries and technologies and also
> lets me develop some of my ideas in terms of structure and layout.
> Once again, I am finding myself visiting the age old problem of
> service interfaces with single implementations. There seems to be
> quite a few ideas on how to deal with this. Some say not to use an
> interface at all and just have the implementation class, some say to
> use an interface, and then there are suggestions for the naming of the
> implementation class, <Interface>Imp­l? Default<Interface­>? Try really
> hard to come up with a prefix or suffix that is less generic?
> Over the years I have flitted back and forward between these options,
> never really finding an answer that was all that satisfactory to me.
> Not using an interface always seems the tidiest in terms of code
> structure, but I find that I run into issues around things like AOP
> proxies and having to use cglib proxies rather than JDK ones, which
> adds a lot of complexity and seems to outright break some things.
> *Impl and Default* seems like a bit of a cop-out, and seem (Impl
> especially) as a bit of a tautology.
> Coming up with a more specific name seems OK but I sometimes struggle
> to do this. My services generally use spring, but 'SpringXyzService',
> seems a bit crappy too, other than this there is usually nothing much
> to distinguish them. They are simply the pretty bog-standard
> implementation of the required interface.
> On my new project, I have been trying something a little different,
> which I think I quite like but is perhaps a little unconventional.
> I have been creating the 'Default' implementation of the interface as
> a package scope inner class within the interface definition itself.
> Like this...
> public interface AccountService {
>    Account createAccount(String­ email);
>    @Service
>    class Default implements AccountService {
>        private Collaborator collaborator;
>        Default(Collaborator­ collaborator) {
>            this.collaborator = collaborator;
>        }
>        public Account createAccount(String­ email) {
>            //Implementation here
>        }
>    }
> }
> This kind of thing seems to work functionally, allows for alternative
> implementations either by creating another implementation of the
> AccountService interface or even by extending the default
> implementation and my unit tests have things like this...
> AccountService accountService = new AccountService.Defau­lt(mockCollaborator);­
> Which actually looks quite pretty to my eyes.
> I appreciate that it is all style really, but I am interested if
> anyone has any thoughts, do you use a standard that I haven't
> mentioned here? Do you have any major objection to my new experimental
> approach (either stylistically or because you happen to know it is
> going to break some feature of some important library)?
> Keen to hear any thoughts that anybody has.
> Regards
> Wes
> --
> Please Note: If you hit "REPLY", your message will be sent to everyone on this mailing list ([address removed])
> http://www.meetup...­
> This message was sent by Wesley Hall ([address removed]) from LJC - London Java Community.
> To learn more about Wesley Hall, visit his/her member profile: http://www.meetup...­
> Set my mailing list to email me
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> Meetup, POB 4668 #37895 NY NY USA 10163 | [address removed]

Gerald Loeffler
mailto:[address removed]

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