Can you please add some details about your environment? Is this a slave build? Which JDK, findbugs, Jenkins, etc. is installed?

I've updated the environment section of the issue. Tell me if you need other details.

Please add the plug-in versions of findbugs and analysis-core. And how do you start Jenkins? java -jar or Tomcat?

Note: does this error occur when Jenkins runs using a JDK 6?

analysis-core : 1.47
findbugs : 4.44
Starting Jenkins in standalone mode (java -jar) or deployed in a Tomcat server leads to the same problem.
I've not tried with a JDK6 yet.

Just made a test with JRE6 : same problem.

According to the stack trace, it seems to be a class loading problem with dom4j.
Using mvn dependency:tree, we can see that dom4j is used twice with 2 slightly different versions:

• dom4j:dom4j:jar:1.6.1:compile is a transitive dependency of org.jvnet.hudson.plugins.findbugs:library:jar:2.0.1-SNAPSHOT
• org.jvnet.hudson.dom4j:dom4j:jar:1.6.1-hudson-3:provided is a transitive dependency of org.jenkins-ci.main:jenkins-core:jar:1.409:provided

In FindBugsParser.readXml(), where the bug occurs, you change the context class loader. And I can see in the stack trace that an async task is launched in a ThreadPoolExecutor, so the thread in the executor is certainly not using the class loader you tried to impose in FindBugsParser.readXml(), isn't it ?
Maybe a quick-and-dirty workaround would be to explicitly exclude dom4j:dom4j:jar:1.6.1 when configuring the findbugs dependency ?

Code changed in jenkins
User: Ulli Hafner
Path:
library/.classpath
library/.project
library/.settings/org.eclipse.core.resources.prefs
library/.settings/org.eclipse.m2e.core.prefs
library/pom.xml
http://jenkins-ci.org/commit/findbugs-plugin/20fcf8f9fc4191842f63f2f3c27b1eb737fca247
Log:
[FIXED JENKINS-15344]: Upgrade to findbugs 2.0.1 and exclude DOM4J
library which is already part of core.

I tested the lattest version of Jenkins (1.484) with all the latest versions of the plugins (including analysis core 1.48 and findbugs 4.45) and unfortunately I still have the same error stack trace...

Ok, I see. I just applied your quick fix with the hope that it will work on your machine...

That was just a (bad) idea... I saw that the PMD plugin also comes with its own version of dom4j, but even if I delete it from the list of installed plugin the error still happens.
Where you able to reproduce this problem on your machine or not ? I may try to build a small example so that you can reproduce the problem on your machine.

That would help. I can't reproduce that problem on my machine up to now...

I can't reproduce this with your example. Is there a findbugs warning in your project? When I run it I get:

[INFO] 
[INFO] --- findbugs-maven-plugin:2.5.2:findbugs (default-cli) @ aggregator ---
[INFO] Fork Value is true
[INFO] Done FindBugs Analysis....
mojoSucceeded org.codehaus.mojo:findbugs-maven-plugin:2.5.2(default-cli)
[FINDBUGS] Finding all files that match the pattern findbugsXml.xml
[FINDBUGS] Parsing 1 files in /Users/hafner/Development/jenkins/jobs/JENKINS-15344/workspace/target
[FINDBUGS] Successfully parsed file /Users/hafner/Development/jenkins/jobs/JENKINS-15344/workspace/target/findbugsXml.xml of module aggregator with 0 warnings.
projectSucceeded net.test:aggregator:0.1-SNAPSHOT
sessionEnded

There is no warning found. I'm using the goals "clean package findbugs:findbugs". What did you use?

I use mvn clean site

Thanks Thomas! Now I can reproduce the problem. Seems that maven-site-plugin is the cause for the exception. I need to investigate how I can update my plug-in to work with the results of this maven plugin.

Until that is fixed, please use the goal 'findbugs:findbugs' to create the FindBugs results. Maybe it would also work if you downgrade to 3.0 maven-site-plugin, see JENKINS-14737.

"mvn clean site" works indeed with maven site plugin 3.0, but not with 3.1 or 3.2.
I have also found another workaround: the bug vanishes if instead of doing "mvn clean site" I do "mvn clean install site" !

Any updates? I just had to downgrade to maven-site-plugin 3.0.

@Falko: did you try the workaround noted by Thomas?

This issue is not on my priority list So feel free to provide a patch if the workaround is not working in your environment...

I tried some ideas to get the plug-in correctly running with new site plugin, however nothing worked. I think that this actually is a problem in the class loaders of the maven plug-in in Jenkins core... Seems that they are new isolated enough.

I can still confirm this on 1.574 with maven-site-plugin 3.3. Also the workaround to additionally invoke the default lifecycle (e.g. "clean package site-deploy") works. Though it would be nice to be able to just do a "clean site-deploy" in a dedicated site job.

Dupliate of JENKINS-13709.