<p>

		Tomcat 5.5 uses Commons Logging throughout its internal code allowing the 

		developer to choose a logging configuration that suits their needs, e.g

		JDK Logging or log4j. Commons Logging provides Tomcat the ability to log

		hierarchially across various log levels without needing to rely on a particular

		logging implementation. Commons Logging is therefore a bridge to other implementations.

		<a href="http://jakarta.apache.org/commons/logging/">Visit the Commons Logging project</a>

		for more information.

	</p>

	<p>

		An important consequence for Tomcat 5.5 is that the <Logger> element found in 

		previous versions to create a localhost_log, is no longer a valid nested element 

		of <Context>. Instead, stdout will collect runtime exceptions and other uncaught

		exception generated by web applications. If the developer wishes to collect detailed internal 

		Tomcat logging (i.e what is happening within the Tomcat engine), then they should configure 

		a logging system such as JDK Logging or log4j as detailed next.

	</p>

	<p>

		One note to point out is that currently, the log4j configuration will not function on

		Tomcat server startup, so JDK Logging is more reliable at this point. This is a known

		issue in the pipeline for fix.

	</p>

	<p>

		In order to configure JDK logging you should have JDK 1.4+. Tomcat 5.5 is intended for

		JDK 5.0, but can be run on JDK 1.4 using a compatibility package.

	</p>

	<p>

		In order to configure JDK Logging, you should find the JDK's logging.properties file. Check

		your JAVA_HOME environment setting to see which JDK Tomcat is using (or maybe JRE 5.0 as Tomcat

		can now run on a JRE from version 5.5). The file will be in <i>${JAVA_HOME}/jre/lib</i>.

	</p>

	<p>

		The default logging.properties specifies a ConsoleHandler for routing logging to stdout and

		also a FileHandler. A handler's log level threshold can be set using SEVERE, CONFIG, INFO, 

		WARN, FINE, FINEST or ALL. The logging.properties shipped with JDK is set to INFO. You

		can also target specific packages to collect logging from and specify a level. Here is how

		you would set debugging from Tomcat. You would need to ensure the ConsoleHandler's level is also

		set to collect this threshold, so FINEST or ALL should be set.

	</p>

	<p><source>org.apache.catalina.level=FINEST</source></p>

	<p>A limitation of JDK Logging appears to be the inability to have per-web application logging, 

		as the configuration is per-VM. It is advisable to use log4j for per-web application logging

		as elabatorated on below.

	</p>

  <section name="Conclusion">

	<p>

		The usefulness of what you will find from internal Tomcat logging is debatable for web 

		applications. Unless a problem with Tomcat itself exists, it is probably not required. 

	</p>

	<p>

		It is much more common and recommended for web application themselves to be configured with

		a logging setup. In the case of JDK Logging, you could setup package loggers to collect logging

		from your own applications, e.g <code>com.mycomp.myapp.level=DEBUG</code>. In the case of log4j, a custom

		log4j.properties file would be placed into your web application's WEB-INF/classes folder and 

		log4j-1.2.8.jar into WEB-INF/lib and the log4j.properties file would setup a set of 

		(normally) file appenders to collect the logging, again with package level setup, e.g

		<code>log4j.logger.org.mycomp.myapp=DEBUG, APPENDER_TO_USE</code>.

	</p>

  </section>