Thursday, September 8, 2011

Assorted facts about JBoss. Fact 3: how to make per-application logging work

01.12.2011. Update: Go read first this post. Then come back here if you want.

I am now busy with some JBoss AS6 related work. One of the things I wanted to be able to do is to have a separate application specific log file. Very easy, very understandable requirement.

Except not under JBoss. It looks like there is a completely new logging subsystem in JBoss AS 6. No advice on how to do it in previous versions would help. And there is not much documentation on how to do it except of some examples here and there and complains that this functionality is broken. There is also a corresponding JBoss issue.

The issue page describes the problem and offers a workaround. The issue is marked as resolved in JBoss AS 6.1.0 Final. The "fix" is actually a proposed workaround; the fact that I immediately did not like.

I have created jboss-logging.xml so that all the logging from my application would go not to ${jboss.server.log.dir}/server.log but to ${jboss.server.log.dir}/my-app.log. After deploying my application I immediately noticed that the fix worked: there was no error. I also got my-app.log next to server.log. All nice and dice. Brand new empty my-app.log no matter what I did in my application. All the logging still went to server.log. So much for the fix.

And it looks like I am not alone. This post mentions the same problem: "My new log file is empty."

But the new wonderful logging subsystem does more for me! When I undeploy my application I get the following exception:
ERROR [org.jboss.deployers.vfs.deployer.kernel.BeanMetaDataDeployer]
Error during undeploy: Logging:REGISTRATION:MyAppLogContext:Anonymous-5: java.lang.NullPointerException
at org.jboss.logging.metadata.GetClassLoaderBeanMetaData.setClassLoader(GetClassLoaderBeanMetaData.java:52)
at org.jboss.deployers.vfs.deployer.kernel.BeanMetaDataDeployer.undeploy(BeanMetaDataDeployer.java:237)
at org.jboss.deployers.vfs.deployer.kernel.BeanMetaDataDeployer.undeploy(BeanMetaDataDeployer.java:58)
Bummer!

After some poking around jboss configuration and the source code I have found a solution. Actually a workaround and a fix.

Workaround:
  1. If you are still working on JBoss AS 6.0.0.Final then you have to apply the workaround described in this issue: change file JBOSS_HOME/server/<servername>/deployers/jboss-logging.deployer/META-INF/logmanager-jboss-beans.xml. Now you have the same configuration as JBoss AS 6.1.0.Final.
  2. Change the logging deployer configuration (file JBOSS_HOME/server/<servername&g;/deployers/jboss-logging.deployer/META-INF/logmanager-jboss-beans.xml) by removing that mode="On Demand" from
    OnDemandJBossLogManagerContextSelector bean:
    <bean name="OnDemandJBossLogManagerContextSelector"
    class="org.jboss.logmanager.LogContextSelectorService"
    mode="On Demand">
    <property name="selector">
    <inject bean="JBossLogManagerContextSelectorService"/>
    </property>
    </bean>
    You can also remove that comment above about lazy loading. It is not true anyway.

Congratulations, you have now your application specific log file and your logging really goes to this file. Unfortunately you will get NPE (see above) when your application is undeployed. This can't be worked around.

The fix is actually a code patch. I have submitted it to JBoss (see here). Unfortunately it means we have to wait until it is accepted and incorporated into some release. For those who are not afraid of javac: you can download the patch from the issue page and build it yourself. You will have to update the logging deployer configuration (file JBOSS_HOME/server/<servername&g;/deployers/jboss-logging.deployer/META-INF/logmanager-jboss-beans.xml). It is also included in the patch.

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