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Re: [ljc] RFC - Default service implementation structure

From: user 1.
Sent on: Friday, March 8, 2013 10:52 AM


Sent from my iPhone

On 8 Mar 2013, at 09:24, Karl Bennett <[address removed]> wrote:

Hi Wesley,

I've thought of using a similar pattern my self and have actually found my self using inner classes a bit more recently for specialist classes.

I don't get why you have given the Default implementations default access though. Wouldn't it be better to have them as public so that they can be used in centralised configuration or extended/utilised by a class outside of the interfaces package?

I don't understand the motivation for the restriction.

Cheers,
Karl


On 8 March[masked]:52, Wesley Hall <[address removed]> wrote:
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
>>>>
>>>>
>>>>
>>>>
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>>>
>>>
>>>
>>> --
>>> Gerald Loeffler
>>> mailto:[address removed]
>>> http://www.gerald-loeffler.net
>>>
>>>
>>>
>>>
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>>
>>
>>
>>
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>> This message was sent by Wesley Hall ([address removed]) from LJC - London Java Community.
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>> Set my mailing list to email me
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>
>
>
> --
> Gerald Loeffler
> mailto:[address removed]
> http://www.gerald-loeffler.net
>
>
>
>
> --
> Please Note: If you hit "REPLY", your message will be sent to everyone on this mailing list ([address removed])
> http://www.meetup.com/Londonjavacommunity/
> 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.com/Londonjavacommunity/members/8654439/
> Set my mailing list to email me
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> Meetup, POB 4668 #37895 NY NY USA 10163 | [address removed]
>




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Please Note: If you hit "REPLY", your message will be sent to everyone on this mailing list ([address removed])
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