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From Emmanuel Lécharny <>
Subject Re: [ADS 2.0] OSGi, interceptors
Date Thu, 13 Oct 2011 12:05:13 GMT
On 10/13/11 1:44 PM, Alex Karasulu wrote:
> On Thu, Oct 13, 2011 at 2:20 PM, Emmanuel Lécharny<>wrote:
>> Hi,
>> Göktük asked if there is a way to transform Interceptors to be bundles
>> instead of being statically loaded in core.
>> I tried to play around the idea yesterday in the train, and I faced some
>> interesting challenges.
>> o First, many interecptors are doing calls to the chain again, but with a
>> restricted set of interceptors. For instance, in the SchemaInterceptor, we
>> go through the chain again when modifying the schema itself. In order to
>> speedup the operation, we declare a BYPASS sets of interceptors (I'm not
>> sure it's a good idea, but right now, this is how we proceed). At the end,
>> this BYPASS set is declared this way :
>>     private static final Collection<String>  BYPASS;
>>     static
>>     {
>>         Set<String>  c = new HashSet<String>();
>>         c.add( AuthenticationInterceptor.**class.getName() );
>>         c.add( AciAuthorizationInterceptor.**class.getName() );
>>         c.add( DefaultAuthorizationIntercepto**r.class.getName() );
>>         c.add( ExceptionInterceptor.class.**getName() );
>>         c.add( SchemaInterceptor.class.**getName() );
>>         BYPASS = Collections.**unmodifiableCollection( c );
>>     }
>> As we can see, it creates a static dependency on interceptors. It might be
>> a better idea to use logical names instead of class names, and let the OSGi
>> container retrieve the classes itself.
> This is a good idea. How about going a little further and having a set of
> interceptor chain re-entry constants or set of enum values like:
> etc ...
> This is like saying we do not need authentication, authorization, additional
> exception handling and checks or schema checking on re-entry instead of
> having a direct list of interceptors to avoid.

That's a good idea.

One thing that might be problematic though is that we have no idea which 
interceptors are going to be present in the chain, so we may be unable 
to tell the chain not to use the interceptors added on the fly (for 
instance, the logger interceptor).

I'd rather create a set of interceptors we want to go through, as we 
know which one we will use in those internal cases.

In any case, using constants instead of class name is the way to go.
> Then Interceptors when they register themselves can announce what standard
> functions they perform according to this set. Some may not announce at all
> if they perform none of these functions. This way the chain determines what
> to include and what to exclude based on these properties. There's no direct
> link with the interceptor itself and any implementation can be swapped in
> and out.
> This way we are letting the interceptor chain devise the proper chain of
> interceptors based on these properties instead of using more explicit names
> or direct references to the interceptor classes.

Ultimately, for each operation (add, delete, lookup, etc), we should be 
able to define the set of interceptors we are going through. This should 
be defined somewhere in the code, not in each interceptors. It may even 
be some configurable information...
> There can also be other hint mechanisms given to the interceptor chain so it
> can correctly asses which interceptors to include or exclude on re-entry.
> For example there could be properties exposed for defaults on the
> interceptor telling the chain always exclude on re-entry etc. There should
> be some more thought put on this but the present situation as you state
> sucks where OSGi and pluggability is concerned.
Right. We will try to get OSGi implemented anyway, and once it's done, 
we can start thinking about a better mechanism.

Emmanuel Lécharny

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