JMX Configurator
As its name indicates, JMXConfigurator
allows
configuration of logback via JMX. In a nutshell, it lets you
reconfigure logback from the default configuration file, from a
designated file or URL, list loggers and modify logger levels.
Using the JMX Configurator
If your server run on JDK 1.6 or later, then you can just
invoke jconsole
application on the commmand line and
then connect to your server's MBeanServer. If you are running an
older JVM, then you should read the section on JMX enabling your server.
JMXConfigurator
is enabled by a single line in
your logback configuration file, as shown below:
<configuration> <jmxConfigurator /> <appender name="console" class="ch.qos.logback.classic.ConsoleAppender"> <layout class="ch.qos.logback.classic.PatternLayout"> <Pattern>%date [%thread] %-5level %logger{25} - %msg%n</Pattern> </layout> </appender> <root level="debug"/> <appender-ref ref="console" /> </root> </configuration>
After you connect to your server with jconsole, on the MBeans panel, under "ch.qos.logback.classic.jmx.Configurator" folder you should see several operations to choose from, as shown in the figure below:
Screen-shot
of JMXConfigurator
viewed in
jconsole

Thus, you can
- Reload logback configuration using the default configuration file
- Reload the configuration with the specified URL
- Reload the configuration with the specified file
- Set the level of a specified logger. To set to null, pass the string "null" as value.
- Get the level of a specified logger. Returned value can be null.
- Get the effective level of a specified logger
JMXConfigurator
exposes the list of existing
loggers and a status list as attributes.
The status list can help you diagnose logbacks internal state.

Avoiding memory leaks
If your application is deployed in a web-server or an
application server, the registration of an
JMXConfigurator
instance creates a reference from the
system class loader into your application which will prevent it
from being garbage collected when it is stopped or re-deployed,
resulting in a severe memory leak.
Thus, unless your application is standalone java application,
you MUST unregister the JMXConfigurator
instance from
the JVM's Mbeans server. Invoking the reset
() method
of the appropriate LoggerContext
will automatically
unregister any JMXConfigurator instance. A good place to reset the
logger context is in the the contextDestroyed
()
method of a
javax.servlet.ServletContextListener
. Here is sample
code:
import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import org.slf4j.LoggerFactory; import ch.qos.logback.classic.LoggerContext; public class MyContextListener implements ServletContextListener { public void contextDestroyed(ServletContextEvent sce) { LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory(); lc.stop(); } public void contextInitialized(ServletContextEvent sce) { } }
JMXConfigurator
with multiple web-applications
If you deploy multiple web-applications in the same server,
then, and assuming you have not overriden the default context selector, and assuming you
have placed a copy of logback-*.jar and
slf4j-api.jar under the WEB-INF/lib folder of
each web-application, by default each JMXConfigurator
instance will be registered under the same name, that is,
"ch.qos.logback.classic:Name=default,Type=ch.qos.logback.classic.jmx.JMXConfigurator". In
other words, by default the various JMXConfigurator
instances associated with the logger contexts in each of your
web-applications will collide.
To avoid such undesirable collisions, you can instruct each
JMXConfigurator
instance to have a different name by
setting the "contextName" attribute of the
<jmxConfigurator>
element in the logback
configuration file.
For example, if you deploy two web-applications named "Koala" and "Wombat", then you would write in Koala's logback configuration
<jmxConfigurator contextName="Koala" />
and in Wombat logback configuration file, you would write:
<jmxConfigurator contextName="Womcat" />
In jconsole's MBeans panel, you would two distinct
JMXConfigurator
instances:

You may fully control the name under which JMXConfigurator is
registered with MBeans server with the help of the "objectName"
attribute of <jmxConfigurator>
element.
JMX enabling your server
If your server runs with JDK 1.6 or later, your server should be JMX enabled by default.
For older JVMs, we suggest that you refer JMX-related documentation of your web-server. Such documentation is available for both Tomcat and Jetty. In this document, we briefly describe the required configuration steps for Tomcat and Jetty.
Enabling JMX in Jetty (tested under JDK 1.5 and JDK 1.6)
The following has been tested under JDK 1.5 and 1.6. Under JDK 1.6 and later, your server is JMX enabled by default and you can, but do not need to, follow the steps discussed below. Under JDK 1.5, adding JMX support in Jetty requires a number of additions to the $JETTY_HOME/etc/jetty.xml configuration file. Here are the elements that need to be added:
<Call id="MBeanServer" class="java.lang.management.ManagementFactory" name="getPlatformMBeanServer"/> <Get id="Container" name="container"> <Call name="addEventListener"> <Arg> <New class="org.mortbay.management.MBeanContainer"> <Arg><Ref id="MBeanServer"/></Arg> <Call name="start" /> </New> </Arg> </Call> </Get>
If you wish to access the MBeans exposed by Jetty via the
jconsole
application, then you need start jetty after
having set the "com.sun.management.jmxremote" java system
property.
For a standalone version of Jetty, this translates to:
java -Dcom.sun.management.jmxremote -jar start.jar [config files]
And if you wish to launch jetty as a Maven plugin, then you
need set the "com.sun.management.jmxremote" system property via
the MAVEN_OPTS
shell variable:
MAVEN_OPTS="-Dcom.sun.management.jmxremote" mvn jetty:run
You can then access the MBeans exposed by Jetty as well as
logback's JMXConfigurator
via
jconsole
.

After you are connected, you should be able to access
JMXXConfigurator
as shown in the screenshot above.
MX4J with Jetty (tested under JDK 1.5 and 1.6)
Ig you wish to acces JMXConfigurator
via MX4J's
HTTP interface and assuming you have already downloaded MX4J, you then need to
modify the jetty configuration file discussed previously by adding
an instruction to set the management port.
<Call id="MBeanServer" class="java.lang.management.ManagementFactory" name="getPlatformMBeanServer"/> <Get id="Container" name="container"> <Call name="addEventListener"> <Arg> <New class="org.mortbay.management.MBeanContainer"> <Arg><Ref id="MBeanServer"/></Arg> <Set name="managementPort">8082</Set> <Call name="start" /> </New> </Arg> </Call> </Get>
Moreover, mx4j-tools.jar needs to be added to Jetty's class path.
If you are running jetty as a Maven plug-in, then you need to add mx4j-tools as a dependency.
<plugin> <groupId>org.mortbay.jetty</groupId> <artifactId>maven-jetty-plugin</artifactId> <configuration> <jettyConfig>path/to/jetty.xml</jettyConfig> ... </configuration> <dependencies> <dependency> <groupId>mx4j</groupId> <artifactId>mx4j-tools</artifactId> <version>3.0.1</version> </dependency> </dependencies> </plugin>
After Jetty is started with the above configuration,
JMXConfigurator
will be available at the following
URL (search for "ch.qos.logback.classic"):
Below is a screen shot view of the MX4J interface.

Configuring JMX for Tomcat (tested under JDK 1.5 and 1.6)
If you are using JDK 1.6 and later, your server is already JMX enabled by default and you can, but do not need to, follow the steps discussed below. Under JDK 1.5, Tomcat requires the addition of the following lines to the $TOMCAT_HOME/bin/catalina.bat/sh shell script:
CATALINA_OPTS="-Dcom.sun.management.jmxremote"
Once started with these options, Mbeans exposed by Tomcat as
well logback's JMXConfigurator
can be accessed with
jconsole
by issuing the following command in a shell:
jconsole

After you are connected, you should be able to access
JMXXConfigurator
as shown in the screenshot above.
MX4J with Tomcat (tested under JDK 1.5 and 1.6)
You might prefer to access JMX components via a web-based interface provided by MX4J. In that case, here are the required steps:
Assuming you have already downloaded MX4J, placethe mx4j-tools.jar file under the $TOMCAT_HOME/bin/ directory. Then, add the following lines to the $TOMCAT_HOME/bin/catalina.sh configuration file:
<!-- at the beginning of the file --> CATALINA_OPTS="-Dcom.sun.management.jmxremote" <!-- in the "Add on extra jar files to CLASSPATH" section --> CLASSPATH="$CLASSPATH":"$CATALINA_HOME"/bin/mx4j-tools.jar
Finally, declare a new Connector
in the
$TOMCAT_HOME/conf/server.xml file:
<Connector port="0" handler.list="mx" mx.enabled="true" mx.httpHost="localhost" mx.httpPort="8082" protocol="AJP/1.3" />
Once Tomcat is started, you should be able to find JMXConfigurator by pointing your browser at the following URL (search for "ch.qos.logback.classic"):
Below is a screen shot view of the MX4J interface.
