When stopping or undeploying my struts 2 web app in Tomcat (7.0.23) I get several severe warnings from tomcat:
SEVERE: The web application [/myapp] created a ThreadLocal with key of type [com.opensymphony.xwork2.inject.ContainerImpl$10] (value [com.opensymphony.xwork2.inject.ContainerImpl$10@1376afa]) and a value of type [java.lang.Object] (value [[Ljava.lang.Object;@15075f9]) but failed to remove it when the web application was stopped. Threads are going to be renewed over time to try and avoid a probable memory leak.
I've hunted all over the web and found this error repeated in several places, but I haven't yet found a solution. I then found some posts that lead me to believe this was a problem in the xwork libs but that it had been resolved in the latest version:
I also found a reference suggesting this could be a problem with using the deprecated FilterDispatcher rather than a StrutsPrepareAndExecuteFilter:
I was originally using Struts 18.104.22.168 and upgraded to the latest (22.214.171.124) which didn't solve the problem, nor did switching back and forth between the FilterDispatcher and StrutsPrepareAndExecuteFilter.
I also tried an IntrospectorCleanupListener as a shot in the dark but to no avail.
If I comment out the StrutsPrepareAndExecuteFilter and deploy/stop the web app, the severe warnings regarding ThreadLocals go away (though obviously my web app no longer works).
I sought further advice on the Struts 2 user mailing list as well as a couple web forums but didn't get any further suggestions other than to file a bug on JIRA.
It seems at least a few others are experiencing the same issue. From my experimentation it seems something related to the StrutsPrepareAndExecuteFilter starts off threads on startup but they are not shut down properly. I could not find any documentation on additional cleanup I might perform to force any threads started by struts to shutdown.