Hi, thank you for your reply. First I'd like to say that I do implement ServletContextListener at all beacause destroy() fires after the tomcat warnings.
That being said, on this website: http://stackoverflow.com/questions/2255884/jython-and-implementing-httpservlet-contextinitialized is written that "You can optionally also let your servlet both extend HttpServlet and implement ServletContextListener" It is also said that "it is not always considered a good practice." Why is that so ? Would that be an explanation why in my case I can access some variables but others not ? Thank you for your help. -----Ursprüngliche Nachricht----- Von: Pid <p...@pidster.com> Gesendet: 26.05.2010 20:45:53 An: Tomcat Users List <users@tomcat.apache.org> Betreff: Re: Stopping a Timer in contextDestroyed() to avoid memory leaks results in a NullPointerException >On 26/05/2010 19:43, devn...@web.de wrote: >> Hi, >> >> Thanks for reading this. >> >> I am developing a webapp and do not understand the following: >> In my app, I create a Timer when the servlet starts. >> When tomcat stops, I try to stop the timer in order to avoid memory leaks. >> >> My question is: why do I get a NullPointerException while trying to access >> mytimer in contextDestroyed(). >> >> The simplified code: >> >> public class myclass extends HttpServlet implements ServletContextListener { >> >> java.util.Timer mytimer; >> int testint; >> >> public void init() throws ServletException { >> mytimer = new Timer("__test__"); >> TimerTask taskPerformer = new TimerTask() { public void run() >> { whatever_function(); } }; >> mytimer.scheduleAtFixedRate(taskPerformer, 10, 10, 864000); >> testint = 12; >> } > >Why mix & match the Servlet and ServletContextListener methods? > > >p > >> public void contextDestroyed(ServletContextEvent event) { >> System.out.println("Inside contextDestroyed, >> testint="+testint); >> try { >> mytimer.cancel(); >> } >> catch (Exception e) { >> System.out.println("An error occurred inside >> contextDestroyed(): "+e); >> } >> } >> >> public void contextInitialized(ServletContextEvent event) { >> // Nothing here >> } >> >> public void destroy() { >> // Nothing here >> } >> } >> >> The Output: >> May 26, 2010 8:06:30 PM org.apache.catalina.core.StandardService stop >> INFO: Stopping service Catalina >> Inside contextDestroyed(), testing=12 >> An error occurred inside contextDestroyed(): java.lang.NullPointerException >> May 26, 2010 8:06:30 PM org.apache.catalina.loader.WebappClassLoader >> clearReferencesThreads >> SEVERE: A web application appears to have started a thread named [__test__] >> but has failed to stop it. This is very likely to create a memory leak. >> >> What disturbs me, is that my other variable "testint" is accessible within >> contextDestroyed, but not mytimer. >> >> If I save my timer in init() like this: >> >> ServletContext sc = getServletContext(); >> sc.setAttribute("mytimer", mytimer) >> >> and if I modify contextDestroyed() so that it accesses my timer through >> ServletContext >> >> ServletContext context = event.getServletContext(); >> Timer mytimer2 = (Timer)context.getAttribute("mytimer"); >> >> then I have no problem stopping it, making the tomcat warning disappear. >> I'd like to understand why it is so. >> >> Thank you very much in advance ___________________________________________________________ GRATIS: Movie-Flat mit über 300 Top-Videos. Für WEB.DE Nutzer dauerhaft kostenlos! Jetzt freischalten unter http://movieflat.web.de
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