2 Sep
2008
2 Sep
'08
4:51 p.m.
+1
On Mon, Sep 1, 2008 at 10:22 PM, Vincent Massol <vincent(a)massol.net> wrote:
On Aug 30, 2008, at 12:28 AM, Vincent Massol wrote:
[snip]
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.
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().
WDYT?
Thanks
-Vincent
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Thomas Mortagne
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? 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.