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Re: [ljc] RFC - Default service implementation structure

From: Colin V.
Sent on: Tuesday, March 5, 2013 11:54 AM
One thing I've been playing around with lately is trying to make my
implementations *not* use the interface name at all and just describe
what they do, although I admit this can get quite hard.

In general I like my implementation to specify exactly *how* that
implements something, examples might be:

RedisBackedAccountSe­rvice
MySqlBackedAccountSe­rvice

etc.

Often I find that if I can't find a good implementation name, it's a
sign that my design is perhaps wrong and maybe this class doesn't have
the responsibility I think it does.

Recently (well, not that recently) I've also not been a fan of
interfaces with names like *Service, *Repository, *Dao etc.  I find
these to lack the level of cohesion I really want and are not making
themselves amenable to use in Lambdas.  So if you were doing a typical
AccountRepository type class instead of:

AccountRepository
   -> load
   -> save
   -> delete
   -> update

(or whatever things you use), I'd have 4 interfaces

AccountFetcher, AccountUpdater, AccountDeleter etc.  The
implementation itself can implement all 4 interfaces, but I definitely
like the way it lets me expose only the behaviour required to a using
class.

Sorry, waffled on a bit there!

On Mon, Mar 4, 2013 at 11:25 AM, 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...­
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>



-- 
Maybe she awoke to see the roommate's boyfriend swinging from the
chandelier wearing a boar's head.

Something which you, I, and everyone else would call "Tuesday", of course.

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