Vincent Massol wrote:
> On Aug 30, 2008, at 12:28 AM, Vincent Massol wrote:
>
> [snip]
>
>>>> For 2) I'd like to propose:
>>>>
>>>> * Create an interface for Velocity APIs. Something like
>>>> VelocityBridge
>>>> (or VelocityAccess or VelocityApi or...). It would be empty.
>>>> * Each component that want to be accessed from velocity will need to
>>>> implement a component implementing VelocityBridge. It'll have a
>>>> role-
>>>> hint being the name under which it'll be access from Velocity.
>>>> * Create a VelocityService class (component) which has a single
>>>> get(String name) method and which uses the ComponentManager to
>>>> look up
>>>> components which implement VelocityBridge using the name as the role
>>>> hint.
>>>> * Put that VelocityService in the Velocity context under the name
>>>> "services".
>>>>
>>>> In practice this means that users will be able to access all our
>>>> components through the VelocityBridge implementations with a syntax
>>>> like:
>>>>
>>>> $services.office.convert(...)
>>>> $services.translation.translate(...)
>>>> ...
>>>>
>>>> Note1: We would need to be careful that it would be forbidden for
>>>> any
>>>> java code to use a VelocityBridge. This is to ensure all code
>>>> logic is
>>>> put into components and not into the bridges. We should use the
>>>> maven
>>>> enforcer plugin to enforce this rule.
>>>> Note2: This means we'll have 2 APIs to maintain: the velocity one
>>>> (the
>>>> bridges) + the "Java"' one (the main components). But I don't see
>>>> any
>>>> other way...
>>>>
>>>> WDYT?
>>> Why we can't just proxy "java" api with secure invocation handlers
>>> with
>>> using annotation rights as proposed some times ago?
>> Yes that's a good question. I'm not sure but suddenly it seemed to
>> me easier to implement this way (less magic).
>>
>> However you're right that this forces to expose the full api in the
>> velocity bridge implementation class.
>>
>>> Anyway, I think it is easier to not use proxy for some cases,
>>> so +1.
>>>
>>> But I think it should be possible to use only one "java" api for some
>>> services.
>> We should have only 1 mechanism so we need to decide.
>>
>> The problem with annotation I guess is when there's a strong
>> impedance mismatch between the Java API and the velocity one. In
>> that case there's no method to attach the annotation too although
>> the class could be used in those cases...
>>
>> The annotation mechanism will require to write some velocity
>> uberspectors to intercept the method calls and redirect to the
>> correct velocity method handler.
>>
>> To be honest, I'm not sure which solution is best. We should
>> probably take an existing module and see what the velocity API would
>> be for it. We could take the rendering module one.
>>
>> I'm not ready to do that just now but I'll try to do the exercise
>> next week.
>
> Ok here's what I propose:
>
> * A module can have one or VelocityBridge components
> * A VelocityBridge component can override or create new methods
> * A VelocityBridge is registered as a component with a role-hint of
> the class being bridged
> * A VelocityBridge has a getName() method. That's the name under which
> it'll be known in velocity (more below)
> * A VelocityBridge has a getWrappedService() method which returns the
> instance of the class being wrapped.
> * There's a MethodSwapUberspector uberspector which has a high
> priority and thus intercepts all calls.
> * On init the MethodSwapUberspector looks for all VelocityBridge
> components and stores them in a hashmap indexed on their names.
> * When "services.<name>.<method>" is called from Velocity, the
> MethodSwapUberspector gets called and it looks in its hashmap for a
> bridge named <name>. If found it looks for the <method> method in that
> class (with the same signature). If found it calls it. If not found it
> tries to call the method directly by calling it on getWrappedService().
Two questions :
* How do you do when you want a method from the wrapped service not be
callable from velocity ? override and throw a specific exception ?
* I guess the velocity bridge would still be the one responsible for
checking programming rights, right ? One would have do something like
@Programming
public void myMethod(){
getWrappedService.myMethod();
}
is this correct ?
Jerome.
>
> WDYT?
>
> Thanks
> -Vincent
>
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