Tomcat throws java.lang.UnsupportedOperationException when my Application is undeployed

Question

When I undeploy my application from Tomcat, I see below errors in Tomcat logs. What could be the issue? How I should fix this issue.

----------------------------Tomcat log ---------------------------

SEVERE: The web application [/dfsmonitor] created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@6ca32e]) and a value of type [com.sun.xml.stream.XMLReaderImpl] (value [com.sun.xml.stream.XMLReaderImpl@e01430]) but failed to remove it when the web application was stopped. This is very likely to create a memory leak.
Jul 1, 2012 10:18:20 PM org.apache.catalina.loader.WebappClassLoader clearThreadLocalMap
SEVERE: Unable to determine string representation of value of type [com.sun.xml.stream.writers.XMLStreamWriterImpl]
java.lang.UnsupportedOperationException
at com.sun.xml.stream.writers.XMLStreamWriterImpl.entrySet(XMLStreamWriterImpl.java:2134)
at java.util.AbstractMap.toString(AbstractMap.java:478)
at org.apache.catalina.loader.WebappClassLoader.clearThreadLocalMap(WebappClassLoader.java:2433)
at org.apache.catalina.loader.WebappClassLoader.clearReferencesThreadLocals(WebappClassLoader.java:2349)
at org.apache.catalina.loader.WebappClassLoader.clearReferences(WebappClassLoader.java:1921)
at org.apache.catalina.loader.WebappClassLoader.stop(WebappClassLoader.java:1833)
at org.apache.catalina.loader.WebappLoader.stop(WebappLoader.java:740)
at org.apache.catalina.core.StandardContext.stop(StandardContext.java:4913)
at org.apache.catalina.core.ContainerBase.removeChild(ContainerBase.java:932)
at org.apache.catalina.startup.HostConfig.undeployApps(HostConfig.java:1357)
at org.apache.catalina.startup.HostConfig.stop(HostConfig.java:1328)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:326)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:142)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1094)
at org.apache.catalina.core.ContainerBase.stop(ContainerBase.java:1106)
at org.apache.catalina.core.StandardEngine.stop(StandardEngine.java:468)
at org.apache.catalina.core.StandardService.stop(StandardService.java:604)
at org.apache.catalina.core.StandardServer.stop(StandardServer.java:788)
at org.apache.catalina.startup.Catalina.stop(Catalina.java:662)
at org.apache.catalina.startup.Catalina.start(Catalina.java:629)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)
Jul 1, 2012 10:18:20 PM org.apache.catalina.loader.WebappClassLoader clearThreadLocalMap
SEVERE: The web application [/dfsmonitor] created a ThreadLocal with key of type [java.lang.ThreadLocal] (value [java.lang.ThreadLocal@1bf8785]) and a value of type [com.sun.xml.stream.writers.XMLStreamWriterImpl] (value [Unknown]) but failed to remove it when the web application was stopped. This is very likely to create a memory leak.
Jul 1, 2012 10:18:20 PM org.apache.coyote.http11.Http11AprProtocol destroy
INFO: Stopping Coyote HTTP/1.1 on http-8080

Please let me know what could be the issue.

Answer 1

You could avoid placing XMLStreamWriterImpl instances into thread locals, that way upon shutdown Tomcat wouldn't have any issues removing them.

But other than actually implementing the destroy method on a Servlet, or registering shutdown hooks in an environment such as Spring and tracking all the values you've ever set into threadlocals just so you can remove them upon shutdown, I don't think you really need to worry about this. Though it is odd that you, or code you're using, is storing this value into a threadlocal - typically stream writers are created and destroyed quickly and don't persist very long.