public void onStartup()

in log4j-jakarta-web/src/main/java/org/apache/logging/log4j/web/Log4jServletContainerInitializer.java [37:69]
28 lines of code
6 McCabe index (conditional complexity)

    public void onStartup(final Set<Class<?>> classes, final ServletContext servletContext) throws ServletException {
        if (servletContext.getMajorVersion() > 2
                && servletContext.getEffectiveMajorVersion() > 2
                && !"true"
                        .equalsIgnoreCase(servletContext.getInitParameter(
                                Log4jWebSupport.IS_LOG4J_AUTO_INITIALIZATION_DISABLED))) {
            final Logger LOGGER = StatusLogger.getLogger();

            LOGGER.debug("Log4jServletContainerInitializer starting up Log4j in Servlet 3.0+ environment.");

            final FilterRegistration.Dynamic filter =
                    servletContext.addFilter("log4jServletFilter", Log4jServletFilter.class);
            if (filter == null) {
                LOGGER.warn("WARNING: In a Servlet 3.0+ application, you should not define a "
                        + "log4jServletFilter in web.xml. Log4j 2 normally does this for you automatically. Log4j 2 "
                        + "web auto-initialization has been canceled.");
                return;
            }

            final Log4jWebLifeCycle initializer = WebLoggerContextUtils.getWebLifeCycle(servletContext);
            initializer.start();
            initializer.setLoggerContext(); // the application is just now starting to start up

            if (!"true"
                    .equalsIgnoreCase(
                            servletContext.getInitParameter(Log4jWebSupport.IS_LOG4J_AUTO_SHUTDOWN_DISABLED))) {
                servletContext.addListener(new Log4jServletContextListener());
            }

            filter.setAsyncSupported(true); // supporting async when the user isn't using async has no downsides
            filter.addMappingForUrlPatterns(EnumSet.allOf(DispatcherType.class), false, "/*");
        }
    }