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From "Marepalli, Somesh" <Somesh.Marepa...@ca.com>
Subject RE: Using log4j for writing a library...
Date Fri, 04 Jun 2004 13:06:10 GMT
   Thanks for the replies. I am planning to use the .properties file
internal to my .jar file (not using log4j default configuration).

   Also, as suggested below, I plan to write a config utility class with
static method. It is in this class I plan to use PropertyConfigurator
  However, instead of user invoking explicit API to configure with the
library provided logging .properties file, I would still like to decide
automatically when to use it. I would like to configure my library using
this internal .properties file when no other logging has been
configured. That's the use case which suits my library.

   From another user's e-mail, there is a thread talking about detecting
if log4j is configured - is that advisable for a library? 

   But from your mail - I am now sure of one thing. If by mistake, log4j
is configured a second time inside the library, the user's root logger
and other loggers would lose the settings from configuring the first

   Is this a correct conclusion?

    Thanks for all the replies...
At 05:33 PM 6/3/2004 -0400, you wrote:
>     I am writing a Java based library for which I am using the log4j
>package (version 1.2.8)
>     I am new to log4j. I am confused about the following points:
>     a) Are there any special things we need to worry about
>        Currently, I am considering configuration from a properties
>using the PropertyConfigurator class when the library
>        initializes.

Sure.  You can use a properties file or XML file

>  I am planning to include a logging .properties file
>within my .jar file for the library.

Bad idea.  Logging is for your users, not for you (unless you are
your library, of course)

>        The case I am considering I when users (read as applications)
>my library may also be using log4j.

Exactly!  You can't know what your users want to log and if you provide
default log4j.properties file in the classpath, then you may end up 
overriding a users own properties file causing the user excessive
as to why Log4j isn't logging the way they have it configured.

>   I am not sure if I
>        use PropertyConfigurator class without resetting logging
>configuration of a user in that case.

This is an even worse idea than providing a properties file which
override a users.  In this case, you are programmatically configuring
and will almost certainly override a users logging configuration, again,

causing excessive confusion for the user.

If you want a compromise, you could maybe provide a default 
log4j.properties file, but don't put it in the root of the jar where
is looking for it.  Then provide a utility class with a static method
as Log4jUtility.configureMyLibrary() which the user can call, if 
desired.  configureMyLibrary() would load up your properties file and 
programmatically configure Log4j.  Since this will be used only with the

user's clear intent, then there should be no confusion, keeping everyone

>        Specifically, I would like all loggers within my library to be
>least at the WARN level. Is there a way I can ensure that
>        even if I am writing a library.

The simple truth is that you shouldn't force your own concept of what
want logged upon your users.  If users want to see logging from your
they can specify your package to be logged (as long as you stick to the 
standard naming conventions for loggers, eg....

>    b) For RollingFileAppender, is there a nice way to specify location
>of log file without hard-coding the path. I am interested in knowing
>what other library writers do in such cases.

Reference the name of a system property and make sure to provide that 
system property either programmatically (before any configuration of
happens) or via the command line such as:

java -Dlog_location=/path/to/log/directory MyClass

In the config file, have something like...


>    Hope the user community can help me with these questions.

I hope I helped!


>Somesh Marepalli

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