Re: [Hivemind] ServiceImplementationFactory - no Exception (?)

[btomasini]

Great!  I may take my hand at a patch, but I fear am too 
new to this project to get my head around it.  Maybe I 
will Bugzilla this one if I have some time.

Great product all in all.  BTW, any thoughts for 
Intializable.initializeService() throwing an exception, 
too?

I don't want to open pandora's box here, but I hit a 
similar issue with that as well.

Ben

On Wed, 17 Mar 2004 23:32:04 -0500
 Harish Krishnaswamy <[EMAIL PROTECTED]> wrote:
Christian is absolutely right, I don't know what I was 
thinking. The conscious decision was about not throwing 
the exception at load time and should always expect to 
see an exception when accessing a service point that has 
no contribution or had problems loading it. Sorry 
Benjamin! That should certainly be a bug.

-Harish

Christian Essl wrote:

But, if I'm a client and I call registry.getService() I 
absolutely 
want a
service or an exception! Otherwise I have to stick null 
checks in all 
over


I agree. Actullay I was always expecting HiveMind to do 
that. This is 
also more consistent, because if the module or the 
ServiceExtensionPoint is not found an 
ApplicationRuntimeException is 
thrown.

But now I am a bit confused about where this null comes 
from. As I see 
all ServiceModels - except of primitive - always return a 
proxy, 
independent of what the factory actually returns. And the 
primitive 
ServiceModel (and as I think the other Models as well) 
uses 
AbstractServiceModelImpl.constructCoreServiceImplementation() 
which 
does check for null and throws an 
ApplicationRuntimeException.

Maybe Benjamin you could tell how you got this null. So 
that it could 
be reproduced on the current HiveMind from the cvs. To me 
it looks 
like a bug. Or maybe you used an 
ServiceImplementationFactory directly 
- Spring like?  Or I just miss something.

Thanks,
Christian
On Wed, 17 Mar 2004 01:34:28 -0500, Geoff Longman 
<[EMAIL PROTECTED]> wrote:

Wait a sec. Sure log errors when the modules are parsed. 
That makes 
sense.

But, if I'm a client and I call registry.getService() I 
absolutely 
want a
service or an exception! Otherwise I have to stick null 
checks in all 
over
the place.

Geoff
----- Original Message -----
From: "Harish Krishnaswamy" <[EMAIL PROTECTED]>
To: "Jakarta Commons Developers List" 
<[EMAIL PROTECTED]>
Sent: Tuesday, March 16, 2004 10:34 PM
Subject: Re: [Hivemind] ServiceImplementationFactory - no 
Exception (?)


Not throwing an exception is a conscious decision. 
HiveMind is a
microkernal to be thought of as a servlet container - it 
loads all
modules at startup and any problems with the descriptors 
will be
identified and logged at load time but will continue to 
run. I can see
an exception being thrown at load time when there is a 
problem but
certainly disagree with the idea of throwing exceptions 
at runtime. 
If a
service is not loaded properly you have two options - 
don't care or fix
it and reload it!

-Harish

Benjamin Tomasini wrote:

I have started to use Hivemind and have been successful 
in porting 
over
some existing work.  It is quite nice!  Very well thought 
out. Keeping
the service / proxy layer in place is cool.

One suggestion so far...

I had a case where my service object from 
Registry.getService came 
back
null.  One of the services used the BuilderFactory.  I 
was getting a
log4j ERROR message, but no exception was thrown to my 
app.  It was a
simple runtime error - a typo in a config file.

Looking further, I see that

in

org.apache.hivemind.ServiceImplementationFactory

the method

createCoreServiceImplementation(....)

does not throw an exception or anything.

It seems that this prevents calling applications from 
knowing about
problems creating a service.  I could always check for 
null in the
service object, but this isn't quite right, IMO. 
Especially with the
lazy loading, I think burying any exception here is bad, 
especially 
for
apps that depend on a large number of services.

I would be willing to put some work into this and submit 
a patch if we
think we need some exception handling here.

Ben

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