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From cost...@covalent.net
Subject Logging: more classloader problems.
Date Thu, 06 Jun 2002 18:08:10 GMT

The problem: it won't work if commons-logging.jar is installed in the 
parent class loader, and log4j.jar ( or another logger ) is installed in 
a child loader ( like WEB-INF/lib ).

What happens:
- the factory uses the thread class loader to check if the log4j ( 
or any other impl. ) exists ( and it does ).

- it creates an instance of the Logger adapter. This will be created
using parent loader ( the one that loads commons-logging ).

- the Logger instance makes references to Category or other classes
that are used in it's implementation. End of story, since the 
class loader can't find the reference.

This works fine for JAXP because the adapter for a parser is part of the 
parser jar. It doesn't work for c-l because the adapter is in the 
root loader ( with the API), not with the logging impl.

That doesn't affect people who just use a single logger or can put
the logger impl. in the same place with common-logging. It only 
affect containers like tomcat, when you want to let each webapp
use it's own logger impl. of choice.

I tried all kind of introspection games, it won't work. The only solution
I see is to make sure the adapters are in the same place with the logger.

Solution:
Split commons-logging.jar in commons-logging-api.jar ( only the API and
the LogFactoryImpl, no adapteer ) and commons-logging-impl.jar. 

Alternatively, leave commons-logging.jar as it is and create a second
commons-logging-api.jar.

The -api will be included in the common loader. Each webapp will have to
include commons-logging.jar ( or -impl ), and it's own logger. 

Or course, the best would be to have the adapter included in the 
logger impl.

What do you think ? Craig, Remy can we make another c-l dot release with 
this change ? ( I'll do some more testing to see how it works )

Costin






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