Hi everyone,
I seem to have a solid understanding problem with the way log4j loads its
configuration, perhaps someone can take a few minutes to explain it to me? I
only started a few hours ago, but I'm already startled... :-|
Basically, what I want to do is create a simple logger and configure it
using an XML file.
So my questions are:
- does log4j have to load a default configuration file (log4j.xml or
whatever I set log4j.configuration to) even if I call the
PropertyConfigurator.configure( String filename ) function??
- This wouldn't be such a problem if I understood clearly how the default
configuration file interacts with another configuration file I might be
trying to load: are the loggers/appenders simply added to the default
configuration, or are there any risks when overwriting parts of it?
A concrete example:
Here's the Java code I'm testing with:
import org.apache.log4j.*;
public class Test {
static Logger
__logger;
public static void main( String args[] ) throws Exception {
// 1
//PropertyConfigurator.configure( "~/log4j_config.xml" );
// 2
BasicConfigurator.configure();
__logger = Logger.getLogger( Test.class );
__logger.info( "bonjour" );
}
}
Pretty basic. Now I have the following file which is used as the default
configuration by specifying -Dlog4j.configuration=log4j_default.xml on the
command line when starting java:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration PUBLIC "-//Apache//log4j LOG4J 1.0//EN"
"http://logging.apache.org/log4j/docs/api/org/apache/log4j/xml/log4j.dtd"; >
<log4j:configuration>
<appender name="stdout" class="org.apache.log4j.ConsoleAppender">
<layout class="org.apache.log4j.PatternLayout">
</layout>
</appender>
<root>
<level value="fatal" />
<appender-ref ref="stdout" />
</root>
</log4j:configuration>
Again pretty easy, and when I execute the program I get the expected output
(i.e. nothing).
Now suppose I have a second file called log4j_config.xml, which is the same
as log4j_default.xml, except that it has an additional entry:
<logger name="Test">
<level value="info"/>
<appender-ref ref="stdout" />
</logger>
After uncommenting the line after // 1 in my code and commenting out the one
after // 2 (i.e., as I understand it, switching from default configuration
to "named" configuration), I find that the normal output hasn't changed a
single bit, although I'd have expected a message "bonjour" to be dumped to
the console (appender "stdout" is registered for logger Test with level
output, which matches the code, doesn't it?). However, the debug output
(enabled with -Dlog4j.debug=1) has changed, below is the output after the
first call (default config) and, in bold, the two lines added after the
second call (file config):
log4j: Trying to find [log4j_default.xml] using context classloader
sun.misc.launcher$appclassloa...@61ba34f2.
log4j: Using URL [file:/home/pagod/projects/Test/log4j_default.xml] for
automatic log4j configuration.
log4j: Preferred configurator class: org.apache.log4j.xml.DOMConfigurator
log4j: System property is :null
log4j: Standard DocumentBuilderFactory search succeded.
log4j: DocumentBuilderFactory is:
com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl
log4j: debug attribute= "null".
log4j: Ignoring debug attribute.
log4j: reset attribute= "false".
log4j: Threshold ="null".
log4j: Level value for root is [fatal].
log4j: root level set to FATAL
log4j: Class name: [org.apache.log4j.ConsoleAppender]
log4j: Parsing layout of class: "org.apache.log4j.PatternLayout"
log4j: Setting property [conversionPattern] to [%d{ABSOLUTE} %5p %c{1}:%L -
%m%n].
log4j: Adding appender named [stdout] to category [root].
log4j: Could not find root logger information. Is this OK?
log4j: Finished configuring.
What's this message about not finding the root logger information? It is
contained in both the default config file and the config file given to
PropertyConfigurator.configure...
And where's my info message??
Now however, if I add the same "Test" logger in my default config file and
carry out exactly the same command, I get a somewhat different output:
log4j: Trying to find [log4j_default.xml] using context classloader
sun.misc.launcher$appclassloa...@61ba34f2.
log4j: Using URL [file:/home/pagod/projects/Test/log4j_default.xml] for
automatic log4j configuration.
log4j: Preferred configurator class: org.apache.log4j.xml.DOMConfigurator
log4j: System property is :null
log4j: Standard DocumentBuilderFactory search succeded.
log4j: DocumentBuilderFactory is:
com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl
log4j: debug attribute= "null".
log4j: Ignoring debug attribute.
log4j: reset attribute= "false".
log4j: Threshold ="null".
log4j: Retreiving an instance of org.apache.log4j.Logger.
log4j: Setting [Test] additivity to [true].
log4j: Level value for Test is [info].
log4j: Test level set to INFO
log4j: Class name: [org.apache.log4j.ConsoleAppender]
log4j: Parsing layout of class: "org.apache.log4j.PatternLayout"
log4j: Setting property [conversionPattern] to [%d{ABSOLUTE} %5p %c{1}:%L -
%m%n].
log4j: Adding appender named [stdout] to category [Test].
log4j: Level value for root is [fatal].
log4j: root level set to FATAL
log4j: Adding appender named [stdout] to category [root].
log4j: Could not find root logger information. Is this OK?
log4j: Finished configuring.
18:34:49,771 INFO Test:13 - bonjour
18:34:49,771 INFO Test:13 - bonjour
Now I get a message that my Test logger has actually been registered -- oh
joy! However, at the end I get two messages :-?
Could it be that I now actually have two loggers with the name "Test"?? And
why didn't the debug output tell me about my Test logger during the previous
run? I can't be that log4j hadn't even tried to load the file -- specifying
the name of a non-existing file leads to a FileNotFoundException, as one
might have expected...
So, could anyone tell me what it is I have so blatantly misunderstood?
Just for fun, I've tried calling LogManager.resetConfiguration() before
calling PropertyConfigurator.configure( String filename ), and then upon
calling the "info" function the following warnings are displayed:
log4j:WARN No appenders could be found for logger (Test).
log4j:WARN Please initialize the log4j system properly.
As it looks, my configuration file hasn't had much of an effect, although it
defines the same as the default config... :-|
I'd be so grateful if anyone could explain this to me!!
Cheers,
pagod
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