[FIXED] No log output on contextDestroyed using ServletContextListener & SLF4J

Issue

I am trying to write a message to the logger that a (Vaadin) servlet has stopped, this using SLF4J and Log4j2.

For this I am using a ServletContextListener which logs a message when the application has started. However I have been unable to get any output when logging inside the contextDestroyed method... Here is my implementation:

@WebListener
public class VaadinLogger implements ServletContextListener {

    private static final Logger logger = LoggerFactory.getLogger(VaadinLogger.class);

    @Override
    public void contextInitialized(ServletContextEvent contextEvent) {
        // Remove appenders from JUL loggers
        SLF4JBridgeHandler.removeHandlersForRootLogger();

        // Install bridge
        SLF4JBridgeHandler.install();

        // Get servlet context
        ServletContext context = contextEvent.getServletContext();

        // Retrieve name
        String name = context.getServletContextName();

        // Log servlet init information
        logger.info("Start \"{}\"", name);
    }

    @Override
    public void contextDestroyed(ServletContextEvent contextEvent) {
        // Get servlet context
        ServletContext context = contextEvent.getServletContext();

        // Retrieve name
        String name = context.getServletContextName();

        // Log servlet destroy information
        logger.info("End \"{}\"{}", name, System.lineSeparator()));

        // Uninstall bridge
        SLF4JBridgeHandler.uninstall();
    }
}

At this point, I'm guessing this is probably because at the point contextDestroyed is called, logging is no longer possible because they have already been destroyed by the garbage collector.

So now my question is, is it possible to either log that the servlet has stopped before the context is destroyed, or make the contextlistener execute before log4j2 loggers are destroyed?

Thanks in advance!

Solution

Since log4j 2.14.1, you can disable the auto-shutdown and add a listener to stop the logger.

<context-param>
    <!-- auto-shutdown stops log4j when the web fragment unloads, but that
         is too early because it is before the listeners shut down. To 
         compensate, use a Log4jShutdownOnContextDestroyedListener and
         register it before any other listeners which means it will shut
         down *after* all other listeners. -->
    <param-name>isLog4jAutoShutdownDisabled</param-name>
    <param-value>true</param-value>
</context-param>    

<listener>
   <!-- ensure logging stops after other listeners by registering
        the shutdown listener first -->
    <listener-class>
       org.apache.logging.log4j.web.Log4jShutdownOnContextDestroyedListener
    </listener-class>
</listener>
<listener>
    <listener-class>
        org.springframework.web.context.ContextLoaderListener
    </listener-class>
</listener>

Answered By - Tim Perry