Re: [e4-dev] Re: CSS relationship to e4 workbench

[Eric Moffatt <emoffatt@xxxxxxxxxx>]

The way we handle this for the legacy
code (also an optional dependency) is that the legacy bundle registers
a service using the org.eclipse.e4.services extension point. Then code
that needs to gets the service from the global context. A returned 'null'
means that the bundle isn't there and the code can take appropriate actions
(if any). This mechanism uses the service layer/context rather than reflection
to determine the availability of the necessary classes. It also avoids
the eager loading cases since services themselves are lazy loaded.

Not sure if this will help in the CSS
case but it might provide some avenues to look at...

Eric

Ed Merks <ed.merks@xxxxxxxxx>
Sent by: e4-dev-bounces@xxxxxxxxxxx

04/07/2009 06:11 AM

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Subject	Re: [e4-dev] Re: CSS relationship to e4 workbench

Gunnar,

Well, you still have to be careful about Java wanting to load classes that
might not be available.  Certainly EMF makes quite heavy use of the
type of pattern you describe, i.e.,  non-reflective code guarded by
tests for availability of the classes used in that code.  That's how
we support stand alone execution with no Eclipse dependencies.  Often
it's necessary to put the logic in a separate class to prevent Java from
eagerly loading it.  It's obviously very important to test for proper
behavior when the classes aren't available.

Cheers,
Ed


Gunnar Wagenknecht wrote: 
Kevin McGuire schrieb:
  
1) The use of optional dependencies is cool, but makes
writing more code
here tricky since it must be reflective which is brutal to write (I
believe Boris has a "reflectify" refactor but that only helps
the first
time and change/debug is still a challenge).  It also is a potential
point of introducing errors if we forget to add the CSS plugins to the
product since the tooling won't warn you of their absence (being optional).
    

The trick is to only use reflection to verify that an optional
dependency is satisfied. Thereafter it's totally fine to call out to a
different class which uses the API provided by the optional dependencies
directly.

An example of this can be found in the Equinox Preferences bundle.
org.eclipse.core.internal.preferences.Activator#start
org.eclipse.core.internal.preferences.Activator#addingService

OSGi services actually do support this very well because you only need
to reference the service class by name.

-Gunnar

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