Re: Choosing logging module Log::Log4perl with subcategories

[imp]

Using the easy interface is a good way to start with Log::Log4perl, but to get much out of it you need to put a little more work into customizing it.

The approach I like is to use the class name as the generic logger, and to create subcategories for the certain types of logs in that class. A recent module I wrote used HTML::Parser for event based parsing, and I wanted to select which events were logged. Here is a very stripped down snippet that shows the logging definitions:

package SomeParser;
use strict;
use warnings;
use Log::Log4perl;
my $logger     = Log::Log4perl->get_logger('parser');
my $logexport  = Log::Log4perl->get_logger('parser.export');
my $logtext    = Log::Log4perl->get_logger('parser.events.text');
my $logstart   = Log::Log4perl->get_logger('parser.events.start');
my $logend     = Log::Log4perl->get_logger('parser.events.end');

# stuff
sub tag_opened {
    my ($self, $parser, $tag, $attr, $text) = @_;
    $logstart->is_debug && $logstart->debug(sprintf "<%s>",  $tag);
}

sub tag_closed {
    my ($self, $parser, $tag) = @_;
    $logend->is_debug && $logend->debug(sprintf "</%s>",  $tag);
}

1;

I follow similar approaches throughout the code so I can selectively enable categories such as 'parser.events'.

Another area that I find useful is to have a base class for my test cases (or a library to load), and have the following snippet in it:

if ($ENV{TEST_VERBOSE}) {
    Log::Log4perl->easy_init({ level => $DEBUG, layout => '#%5p %F(%L)
+ - %m%n'});
}
else {
    Log::Log4perl->easy_init({ level => $WARN, layout => '#%5p %F(%L) 
+- %m%n'});
}

This will set the log level to debug when the tests are run in verbose mode (e.g. prove -v t/*.t), otherwise it will be set to warn. In both cases it will have a # before the log message to fit in with the TAP output.