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Re: [ljc] RFC - Default service implementation structure

From: Wesley H.
Sent on: Thursday, March 7, 2013 5:20 PM
I would actually be interested to try this out.

I am not sure it really is that clever of spring really. Inner classes
(to my knowledge) are all just compiler magic. Post-compilation there
isn't really anything different about them, and I *think* that my
static inner implementation results in exactly the same compiler
output as if I had created a top-level class called
AccountService$Defau­lt.java in the same package.

With this in mind I think you would have to go to extra effort to
exclude these classes from runtime annotations scanning (by rejecting
classes with $ in the name for example).

I am about 80% sure of this but someone with better knowledge of the
JVM (ping: Ben or Martijn) can probably confirm.

Wes

On Thu, Mar 7, 2013 at 4:30 PM, Gerald Loeffler
<[address removed]> wrote:
> On Thu, Mar 7, 2013 at 12:36 PM, Wesley Hall <[address removed]> wrote:
>> I am using DI with the spring annotations, spring has no problem
>> finding annotated static inner-classes though I am not sure about
>> other technologies.
>
> that's surprisingly clever of Spring (and not atypical for the
> attention to detail they typically show).
> For EJB and CDI, however, i'm certain that the specs demand that
> auto-discovered components are top-level classes. And i'd be surprised
> if this were different for JAX-WS and JAXRS webservice implementations
> (although i don't remember what the spec says).
>
>> I guess non-static inner classes will not work because they need a
>> reference to the containing instance.
>
> sure.
>
>   cheers
>   gerald
>
>>
>>
>>
>> On Thu, Mar 7, 2013 at 10:55 AM, Gerald Loeffler
>> <[address removed]> wrote:
>>> 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.
>>>
>>>   cheers
>>>   gerald
>>>
>>>
>>> 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
>>>>
>>>> As they are sent
>>>> http://www.meetup...­
>>>>
>>>> In one daily email
>>>> http://www.meetup...­
>>>>
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>>>> http://www.meetup...­
>>>> Meetup, POB 4668 #37895 NY NY USA 10163 | [address removed]
>>>>
>>>
>>>
>>>
>>> --
>>> Gerald Loeffler
>>> mailto:[address removed]
>>> http://www.gerald...­
>>>
>>>
>>>
>>>
>>> --
>>> 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 Gerald Loeffler ([address removed]) from LJC - London Java Community.
>>> To learn more about Gerald Loeffler, visit his/her member profile: http://www.meetup...­
>>> Set my mailing list to email me
>>>
>>> As they are sent
>>> http://www.meetup...­
>>>
>>> In one daily email
>>> http://www.meetup...­
>>>
>>> Don't send me mailing list messages
>>> http://www.meetup...­
>>> Meetup, POB 4668 #37895 NY NY USA 10163 | [address removed]
>>>
>>
>>
>>
>>
>> --
>> 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
>>
>> As they are sent
>> http://www.meetup...­
>>
>> In one daily email
>> http://www.meetup...­
>>
>> Don't send me mailing list messages
>> http://www.meetup...­
>> Meetup, POB 4668 #37895 NY NY USA 10163 | [address removed]
>>
>
>
>
> --
> Gerald Loeffler
> mailto:[address removed]
> http://www.gerald...­
>
>
>
>
> --
> 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 Gerald Loeffler ([address removed]) from LJC - London Java Community.
> To learn more about Gerald Loeffler, visit his/her member profile: http://www.meetup...­
> Set my mailing list to email me
>
> As they are sent
> http://www.meetup...­
>
> In one daily email
> http://www.meetup...­
>
> Don't send me mailing list messages
> http://www.meetup...­
> Meetup, POB 4668 #37895 NY NY USA 10163 | [address removed]
>

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