Re: Is the Checkstyle project interested in a Log4J Best Practice checker?

I am interested in this kind of check.  How Log4j dependent are they?  We
use Slf4j and Logback - would they work with that?


-----Original Message-----
From: Klaus-Peter Berg [mailto:[email protected]] 
Sent: Tuesday, December 09, 2008 2:22 AM
To: [email protected]
Subject: [Checkstyle-user] Is the Checkstyle project interested in a Log4J
Best Practice checker?

Hello,

I have written a Checkstyle-4.4 compatible Log4jCheck (together with some
JUnit tests) to address some logging, i.e., Log4J, "best practices":

+ Logger category according to Fully Qualified Class Name(FQCN) 
+ Logging performance: isDebugEnabled() etc. 
+ Avoid logging inside loops (but logs inside a catch block are allowed) 
+ Avoid logging together with exception propagation (?log & propagate?) 
+ Avoid usage of System.out/err.println() & e.printStackTrace() when you
decided to use logging 

I want to explain these rules shortly:

* You should decide on a naming scheme that assigns each log message to a
particular Logger (Category). Common practice: Use the fully qualified name
of a class as the logger name, and declare the logger as private static
final, e.g. private static final Logger LOGGER =
Logger.getLogger(MyClass.class);
This allows developers to fine-tune log settings for each class (this kind
of Category name is also ?refactoring-safe?). The downside: beware of
copy/paste errors that could lead to a wrong class name as the argument of
Logger.getLogger(..)! So, it should be checked that this class is the same
as the source file tells us. 

* Avoid using parameter construction within the logging request
==> check if the log level is enabled before trying to log! (at least for
info/debug/trace messages), e.g., using "if (LOGGER.isDebugEnabled() {?}"
(of course, if you are logging only a String constant this rule does not
fit) 

*Info, debug, and trace logs should not be included in loops with
potentially large number of iterations (from the Log4J manual: ?Inserting
logging statements in tight loops or very frequently invoked code is a
lose-lose proposal?); such log statements can pollute your log file!
Even be careful to log ERROR/WARNING messages in loops; maybe it is better
to produce a ?summary? to be logged outside the loop 

*Avoid log-and-propagate
Sometimes exceptions are logged AND propagated to the caller. But the caller
(e.g., another developer) is not aware of the logging process already
performed. So he/she may repeat this process (?log-and-propagate?) what
leads to multiple entries in the log file for the same problem! 

Additional rules that fall into this category a looking for
System.out.println/System.err.println and e.printStackTrace() that can
easily be checked with a slightly modified Checkstyle "Generic regex" rule
to avoid "false positives" when such println calls are made inside comments.

The current module is tailored to check Log4J but I think it could be
extended to look at Sun's Java util logging as well.

For more information see my blog entry at
http://www.javaworld.com/community/node/1882.

Please contact me if the Checkstyle project is interesed in this additional
module...

--Klaus
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