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From "Scott Deboy" <sde...@comotivsystems.com>
Subject RE: A Multiplex Appender
Date Fri, 15 Oct 2004 14:20:53 GMT
Great idea..it should support multiple selector keys (hostname.app etc)

Scott


-----Original Message-----
From:	Paul Smith [mailto:psmith@aconex.com]
Sent:	Thu 10/14/2004 9:15 PM
To:	log4j-dev@logging.apache.org
Cc:	
Subject:	A Multiplex Appender
Hi all,

I've been mulling over this whole "I need logs from each User to go in their
own Log file" problem that crops up from time to time.  It seems to be a
common request, even if many of us actually do this differently (e.g. use
MDC in the PatternLayout to interleave the logs).

Anyway, I have been playing around for the last couple of days with a
MultiplexRollingFileAppender, which I think might be useful for inclusion in
log4j1.3.

Summary
=======

org.apache.log4j.rolling.multiplex.MultiplexRollingFileAppender extends from
AppenderSkeleton (it's possibly badly named, and might benefit from being in
a different package)

It is given an instance of a MultiplexSelector instance which the appender
uses to "select" which internal appender should be used for a LoggingEvent,
should this selector not have anything to match, the Selector uses an
instance of an AppenderFactory (also set as a property on
MultiplexRollingFileAppender) to create one and register with the internals
of the Selector.

For convenience I've then given MultiplexRollingFileAppender some special
properties that can automatically create a selector based on an MDC key
value (say "User" for selecting an appender based on the MDC value mapped to
the "User" key).  You can also set the class name of the AppenderFactory to
use as a property in the same way as the ObjectRenderer is created, and I've
created some utility methods in an AppenderFactoryUtils class that can
create an AppenderFactory that uses the MDC key of choice and rolls daily
(probably the most standard pattern) so that all the user needs to do is
create a simple impl of AppenderFactory to delegate to the utility methods
if that matches their use case.

To summarise how I would see the user configuring this in, say
log4j.properties:

log4j.appender.multiplex=org.apache.log4j.rolling.multiplex.MultiplexRolling
FileAppender
log4j.appender.multiplex.MDCSelectorKey=User
log4j.appender.multiplex.AppenderFactory=com.mycompany.myproject.MyMultiplex
AppenderFactory


The user would then need to create the MyMultiplexAppenderFactory class as
so (this example creates a non-rolling simple FileAppender):

public class MyMultiplexAppenderFactory implements AppenderFactory {

	public Appender create(LoggingEvent e) {
		String mdcKey = e.getProperty("User");
 		return AppenderFactoryUtils.
				createSimpleMDCbasedFileAppender(
					"output/MultiplexRollingFileAppenderTestMDC",
					mdcKey,
					new PatternLayout("%m%n")
		);
	}
}


Using the above would create files like:

output/MultiplexRollingFileAppenderTestMDC-Bob.log
output/MultiplexRollingFileAppenderTestMDC-Jane.log
output/MultiplexRollingFileAppenderTestMDC-Alice.log

All based on the value of the MDC key requested.

The source code for all this is all sitting ready to commit.  I have some
basic test-cases, but I wouldn't call them comprehensive, and the JavaDoc
needs a fair bit of work.  Since the AppenderFactory isolates how the
appender is created, one isn't forced to use an Appender of any type, and
you can create your own as needed , this is why it probably should not have
the word "rolling" in it, no should it probably sit in this package.  I
could create a sub-class that did the standard pattern of just using a MDC
Key value, and always rolling every night for those users who want things
simple.

Questions:

1. Should I bother committing this?
2. If so, should it go in the sandbox first?
3. Any thoughts on the design etc?

cheers,

Paul Smith



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