Exposing classes with Merlin

["Noel J. Bergman" <no...@devtech.com>]

> The level of exposure of these classes to client code is a function of
> the container support for isolation.  If your running James in Phoneix
> then these classes will be exposed. If you running under Merlin then
> they will be isolated to the implementing container. For example, under
> Merlin the only API exposed by James is the mailet API.  This enables
> Merlin to export the Mailet API to any component providing that the
> importing component includes the Mailet API in its classloader.
> Everything else is isolated within a James container.

What about James components that use commons-collections, commons-pool,
commons-net, commons-dbcp?  And what do we need to do about exposing those
classes to mailets where a mailet wants to access a common class?

I guess setting up the environment for Merlin is going to be an interesting
excercise.  Obviously you've done it sufficient for your needs.  :-)

	--- Noel


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Re: Exposing classes with Merlin

[Stephen McConnell <mc...@apache.org>]

Noel J. Bergman wrote:

>>The level of exposure of these classes to client code is a function of
>>the container support for isolation.  If your running James in Phoneix
>>then these classes will be exposed. If you running under Merlin then
>>they will be isolated to the implementing container. For example, under
>>Merlin the only API exposed by James is the mailet API.  This enables
>>Merlin to export the Mailet API to any component providing that the
>>importing component includes the Mailet API in its classloader.
>>Everything else is isolated within a James container.
>>    
>>
>
>What about James components that use commons-collections, commons-pool,
>commons-net, commons-dbcp?  And what do we need to do about exposing those
>classes to mailets where a mailet wants to access a common class?
>

You don't - pure and simple.

James uses a bunch of implementation classes and components packaged in a
a number of different components with particular versions and specific
implementation dependencies.  None of that should be exposed to a mailet
implementation.  For example, you james implementation may be dependent on
the latest greates 4.1.5 framework release - but a mailet implementation
does not need to know this.  In fact, the mailet implementation can use
whatever it likes providing that the common API classes are consistent.

This means that James can change with practically zero impact on the
mailet implementation.

"But" you say!!

And before you ask the question concerning the sharing of resources ... 
well,
the physical resources are sharable because thay are accessible via a local
resource repository (which is independent of sharing at the level of
classloaders).  If mailet needs commons collections, it just includes a
resource reference in its classpath defintion.  The resource is cached
locally and accesible by any component implementation.


>I guess setting up the environment for Merlin is going to be an interesting
>excercise.  Obviously you've done it sufficient for your needs.  :-)
>  
>

There is still a lot of scope for exploring posssiblities for mailet 
management that I have not even looked at.  Currently I'm simply 
deploying james in much the same way that Phoenix does - but there is so 
much more potential when you look at james as a coposite component.

Cheers, Steve.



>	--- Noel
>
>
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>  
>

-- 

Stephen J. McConnell
mailto:mcconnell@apache.org




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Re: Exposing classes with Merlin

[Larry Weber <la...@yahoo.com>]

"Noel J. Bergman" <no...@devtech.com> wrote:
> The level of exposure of these classes to client code is a function of
> the container support for isolation. If your running James in Phoneix
> then these classes will be exposed. If you running under Merlin then
> they will be isolated to the implementing container. For example, under
> Merlin the only API exposed by James is the mailet API. This enables
> Merlin to export the Mailet API to any component providing that the
> importing component includes the Mailet API in its classloader.
> Everything else is isolated within a James container.

FYI - should anyone care, which I doubt, Merlin was the internal codeword at AT&T for the PBX System 25. It was the most dubious part of the furry animal series, Antelope (System 85), Gazelle (System 75), and the three-toed Sloth (Net 1000).



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