Does Tomcat have built-in logging capabilities, and if so how do I
use them?
The Servlet Specification requires Servlet Containers like Tomcat to provide
at least a rudimentary implementation of the ServletContext#log method. Tomcat
provides a much richer implementation than required by the Spec, as follows:
- Prior to Tomcat 5.5, Tomcat provided a
Logger element
that you could configure and extend according to your needs. If you
are using a Tomcat version previous to Tomcat 5.5, make sure to read
the Logger configuration reference.
- Starting with Tomcat 5.5,
Logger was removed and
Jakarta Commons-Logging
Log is used everywhere in Tomcat. Read the Commons-Logging documentation
if you'd like to know how to better use and configure Tomcat's internal logging.
In addition, Tomcat does not swallow the
System.out and
System.err
JVM output streams. You may use these streams for elementary logging if you wish, but a
more robust approach such as commons-logging or
Log4J is recommended for production
applications.
How do I configure commons-logging for use with Tomcat?
You need to specify a commons-logging configuration file and, if you wish, a
logging implementation that supports commons-logging. JDK 1.4 (and later)
java.util.Logging and
Log4j
are the two most commonly used logging toolkits for Tomcat. If you supply
an external logging toolkit such as Log4J, it needs to be located in the
$CATALINA_HOME/common/lib directory (for Tomcat 5.0 and earlier) or added
to the bootstrap classpath by using the scripts in $CATALINA_HOME/bin (this
is required for Tomcat 5.5 and later, which uses commons-logging while bootstrapping,
and optional for Tomcat 5.0 and earlier).
For more detailed instructions, see these mailing list discussions:
How should I log in my own webapps?
While you can use
System.out and
System.err to log, we strongly recommend using a toolkit like
Log4J or JDK 1.4's
java.util.logging package. With these toolkits, you have significantly more functionality (for example, sending emails, logging to a database, controlling at runtime the logging level of different classes, inspecting the logs with a graphical viewer, etc.) than with Tomcat's built-in default logging configuration.
We also recommend that you separate your logging from Tomcat's internal logging. That means you should bundle your logging toolkit with your webapp. If you're using Log4J, for example, place the Log4J jar in the WEB-INF/lib directory of your webapp and the Log4J configuration file in the WEB-INF/classes directory of your webapp. This way different web applications can have different logging configurations and you don't need to worry about them interfering with each other.
Where does System.out go?
How do I rotate catalina.out?
System.out and
System.err both print to
catalina.out. But you can suppress this via the swallowOutput property and
sent to different log files.
catalina.out does not rotate. But it should not be an issue because
nothing should be printing to standard output since you are using a logging
package, right?
a thread about rotation of catalina.out
Where are the logs when running Tomcat as a Windows service?
See these mailing list archive threads:
Are there external documents, tutorials, or references about logging in Tomcat?
Yes, there are. You can Google for more, but some such references are:
