[jira] [Created] (WICKET-6519) Internal destroy tries to load classes after WAR is removed.

["Richard O'Sullivan (JIRA)" <ji...@apache.org>]

Richard O'Sullivan created WICKET-6519:
------------------------------------------

             Summary: Internal destroy tries to load classes after WAR is removed.
                 Key: WICKET-6519
                 URL: https://issues.apache.org/jira/browse/WICKET-6519
             Project: Wicket
          Issue Type: Bug
          Components: wicket
    Affects Versions: 7.9.0
         Environment: Tomcat 9.0.2, Ubuntu 16.04, Java 1.8
            Reporter: Richard O'Sullivan


When undeploying a Wicket web application from Tomcat by _removing the war file_ from the deploy sub-directory (in other words, a hot undeploy), a FileNotFoundException prevents Wicket from shutting down properly.

The exception is caused when Wicket's internalDestroy() method needs classes that have _not yet been loaded_ and the class loader attempts to load them from the (now) undeployed war file.

A work around is to preload the classes that Wicket will need during the destroy phase. I was able to resolve the issue using these class loader statements in the init() method of my Wicket WebApplication implementation:
{code:java}
getClass().getClassLoader().loadClass("org.apache.wicket.ApplicationListenerCollection$2");
getClass().getClassLoader().loadClass("org.apache.wicket.core.util.lang.PropertyResolver");
getClass().getClassLoader().loadClass("org.apache.wicket.core.util.lang.PropertyResolver$IPropertyLocator");
{code}
The internalDestroy() method is called from org.apache.wicket.protocol.http.WicketFilter.destroy() in a 'try...finally' block that does not log the Exception. Wicket discourages overwriting this method but doing so allows the stack trace to be logged, as follows:
{code:java}
@Override
public void internalDestroy()
{
    log.info("internalDestroy: ENTER");
    try
    {
        super.internalDestroy();
    }
    catch ( Exception ex )
    {
        ex.printStackTrace();
        throw ex;
    }
    log.info("internalDestroy: EXIT");
}
{code}
Note: For additional troubleshooting, Tomcat provides a 'find leaks' feature on its 'Application Manager' page that reports issues when Wicket fails to undeploy properly.



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